Custom Neoprene Gaskets for Caravan and RV AC Connections

Caravans and motorhomes present the most demanding window seal environment for portable AC connections: the window frames are non-standard in almost every dimension, the installation must survive road vibration and wind loading at highway speed, insects and rodents actively seek any unsealed gap in the vehicle envelope, and the seal must be removable for towing without leaving any projection that could catch air and damage the unit or the window frame. Standard fabric accordion panels designed for domestic windows are entirely unsuitable for this application — they are sized for residential window openings, provide no pest resistance, and vibrate destructively at motorway speed.

Custom-cut neoprene gaskets represent the correct engineering solution for a caravan window split AC gasket seal. Neoprene — polychloroprene synthetic rubber (CR), a polymer with excellent resistance to UV radiation, ozone, temperature extremes, oils, and mechanical abrasion — is used in marine and automotive sealing applications precisely because it combines the flexibility needed to fill irregular contact surfaces with the dimensional stability needed to maintain compression under vibration. For caravan AC sealing, the same properties that make neoprene the material of choice for boat hatch seals make it the best available option for RV window penetration gaskets.

Why do standard foam AC seal kits fail in caravan and RV applications?

Standard foam AC seal kits fail in caravan applications for four distinct reasons. First, the fabric or foam accordion panel is dimensioned for domestic window widths of 500–900 mm, while RV window openings are typically 300–500 mm wide and follow proprietary profiles specific to each caravan manufacturer and model year — there is no standard RV window size that a generic panel fits. Second, the polyester foam material in stock kits degrades rapidly under UV exposure: a summer on a south-facing caravan awning causes visible yellowing and compression set within 60–90 days, after which the foam no longer seals the gap it was compressed into. Third, foam provides no pest resistance — insects, particularly wasps and hornets seeking nesting sites, and small rodents seeking warmth can push through soft foam easily. Fourth, at highway speeds of 100–130 km/h, the loose fabric panel vibrates at resonant frequencies that progressively work the hose collar loose from its grommet.

Neoprene sheet gaskets address all four failure modes. They are cut to the exact profile of the specific RV window opening, with the AC duct slot positioned to match the unit's connection point. They are UV-stabilised and retain their elastic properties across the −30°C to +120°C temperature range — more than sufficient for caravan use across all European seasons. Their closed-cell structure at Shore A 50–60 hardness resists insect and rodent penetration; even the thinnest 3 mm neoprene sheet resists a wasp's mandible without damage. And neoprene's damping properties absorb road vibration rather than resonating with it, maintaining consistent sealing force against the duct regardless of driving surface quality.

The structural difference between a soft foam pad and a correctly specified neoprene gasket becomes apparent within a single driving season. Owners who have switched from foam to neoprene seals consistently report the elimination of the whistling noise that results from air flowing past a partially loose foam collar at highway speed — a noise that typically develops within the first 1,000 km of driving with a foam-sealed AC connection and worsens progressively as the foam fatigues.

How do you cut and profile a neoprene gasket for a specific RV window?

Custom cutting a neoprene gasket for an RV window requires a paper template of the window opening, a sheet of neoprene in the correct grade and thickness, a sharp utility knife or scalpel, a metal straightedge, and a hole punch or jigsaw for the duct opening. The paper template is made by pressing a sheet of paper against the window frame rebate (the recessed seat into which the gasket will compress) and tracing the inner edge of the rebate with a pencil — taking care to capture any irregular corners, drainage channels, or mounting screw locations that the gasket must accommodate. The tracing is transferred to the neoprene sheet and cut with a sharp knife using a metal rule as a guide.

Neoprene sheet is available in multiple grades for RV sealing applications. For this application, a 40–60 Shore A hardness (Shore A is the durometer scale for measuring rubber hardness; 40 is comparable to a pencil eraser, 60 is comparable to a car tyre tread) in a 4–6 mm thickness provides the correct combination of flexibility for installation and stiffness for pest resistance. Thinner sheet (2–3 mm) is too flexible to maintain sealing force against the duct at road vibration frequencies; thicker sheet (8 mm or above) is difficult to compress into the window frame rebate and may prevent the window from closing fully.

The flat duct slot is the most critical cut in the gasket. For a Midea PortaSplit-type flat duct, the slot dimensions are 29 mm × 97 mm. The slot must be cut cleanly — a rough or torn edge allows air (and insects) to enter along the duct body. Use a fresh knife blade, a metal rule as a guide for the long cuts, and a 6 mm diameter hole punch for the four corners of the slot to prevent tearing. After cutting, the slot edge should be burnished smooth with the back of the knife blade to close any surface-cut roughness in the neoprene cell structure.

How do you ensure the gasket stays in place during road travel?

A custom-cut neoprene gasket held only by compression against the window frame rebate will stay in place during road travel if the compression force is sufficient — typically 30–50 N per 100 mm of perimeter length for a correctly specified gasket in a clean rebate. However, European motorway driving at 130 km/h generates aerodynamic pressure fluctuations across the caravan skin that can periodically unload the gasket compression and allow the gasket to shift if it is not positively retained. The solution for road travel is to apply a 10 mm bead of non-permanent silicone sealant — the type sold as kitchen and bathroom sealant, which adheres to both neoprene and aluminium frame surfaces and can be cut away cleanly with a knife at end of season — along the outdoor face of the gasket perimeter before driving.

The non-permanent silicone bead approach provides a weather seal on the outdoor face, a vibration damper at the gasket-to-frame interface, and an aerodynamic seal against wind pressure fluctuations, while remaining fully removable at season's end by cutting along the silicone bead with a sharp knife and peeling. This technique is standard practice in motorhome roof vent sealing and translates directly to window AC gasket applications. The silicone bead should be renewed each season as the adhesion bond gradually weakens with UV exposure and thermal cycling.

For the duct connection itself, the flat refrigerant duct should be supported at the gasket face by a cable clip or saddle clamp screwed or riveted to the window frame, preventing the duct's weight and road vibration from applying shear force to the gasket slot edges. Without this support, the 200–350 g per metre weight of the flat duct creates a downward pull on the slot edges during cornering and braking that progressively tears the neoprene at the slot corners, even through the reinforced corner punched holes.

Pest exclusion beyond the gasket: the wasp nest discovery that most caravan owners make in spring

The neoprene gasket seals the window opening around the duct, but the duct connection itself — where the flat duct enters the outdoor unit's connection port — is a secondary pest entry point that most owners discover when they find a wasp colony in the outdoor unit housing in spring after winter storage. Wasps and hornets, seeking sheltered cavities for nest construction during late summer and autumn, enter through the connection port gap between the duct and its collar fitting and build comb structures in the outdoor unit's fan and condenser section, which can block airflow, damage fan blades, and contaminate the heat exchanger with nest material.

The solution is to fit a fine stainless steel mesh (0.5–1.0 mm aperture) over the outdoor unit's air intake and exhaust grilles during storage, secured with cable ties. Before each season's use, remove the mesh and inspect the outdoor unit fan section for any nest material — even partial nest construction from a brief occupancy period can leave enough debris to imbalance the fan blade and cause vibration. A 15-minute inspection and clean at the start of each season prevents the compressor damage that results from sustained fan imbalance.

Cut a neoprene gasket from a roll of 5 mm sheet and it is the best decision I ever made for the caravan. Zero whistle on the motorway, no insects in the unit at the end of summer, and it peels out cleanly every winter when I store the AC. The foam one I used before was destroyed by the first summer.

What maintenance does a neoprene gasket require between seasons?

1. At end of season: cut away the non-permanent silicone bead from the outdoor face using a sharp knife; clean both gasket faces with isopropyl alcohol to remove road grime and silicone residue.
2. Inspect for compression set: check that the gasket thickness has not permanently reduced below 80% of its original dimension (compression set — permanent deformation caused by sustained compression — reduces sealing force over multiple seasons).
3. Apply a thin coat of rubber protectant or 303 Aerospace Protectant to both faces before storage to prevent ozone-induced surface cracking during winter storage.
4. Store the gasket flat, away from direct UV exposure, in a cool dry location — do not fold or roll tightly, as neoprene can develop permanent creases if stored folded under load.
5. At the start of next season: verify gasket dimensions against the original template; replace if compression set has reduced thickness below 3.5 mm for a 5 mm original gasket (30% compression set threshold).

The bottom line on caravan window split AC gasket seals

A custom-cut 4–6 mm neoprene gasket at Shore A 50–60 is the correct engineering solution for a caravan or RV window split AC seal — not because it is the simplest option, but because it is the only option that simultaneously addresses the sealing, pest resistance, UV durability, and road vibration requirements specific to mobile accommodation. The template-cut and knife-trimmed approach requires a morning's careful work but produces a seal that outperforms any commercial foam alternative within the first driving season.