One consequence of cutting the Beetle in half is that a new barrier between the inside and outside is created along the truck bed front wall. The chassis under the truck bed is filled with holes and inaccessible cavities so keeping water out is an important matter. See also sunroof drains.

Areas that require water management attention

Of primary concern is the long seam of the front truck bed wall that communicates directly with the rear interior floor/carpet as well as the large side channel opening by the rocker panels.

Side channel would drain into the cabin

The side channel slopes down towards the cabin and, if exposed to the weather, would become a catchment for water from the front third of the truck bed undercarriage area. This would result in water draining onto the carpet near the seat belt floor anchors.

Mitigation of this issue is an absolute necessity.

Drainage redesign

VW engineers never considered the need for significant luggage area water drainage. There are two small drains holes on the left and right — one over the gas tank and the other by the exhaust heat shield — but these would not draw water away from the lower channels near the rocker panels.

Wall dam

One approach would be to add a “wall dam” that extends down from the front part of each side wall.

Wall dam side view

The “dam” would create a “wet” middle compartment, leaving the right and left sides by the rocker panel “dry”.

Wall dam boundary line

An added benefit is that the dam would create a waterproof area for mounting the rear speakers through the front truck bed wall.

Channel dam

Channel dam near seat belt anchor

A second smaller dam is added protection against water flowing down the side channel slope. Although this area should be “dry” due to the protection of the larger wall dam, this is an insurance policy against any water that does make it into the side channel. When the cavity is filled with foam, the result should be waterproof.

Side cavity treatment

Side cavity filled with 3M foam

Cavity riveted cover plate

The large side cavity that drains directly into the cabin clearly needs to be addressed. One method is to fill it with 3M foam and then rivet on a top cover. This will prevent water from oozing down inside in the cabin.

Sealing the edges along the truck bed front wall and installing the wall dam are still necessary.

After all the chassis holes are covered (except for the three drain holes — one in the spare tire hold and two towards the front), the entire under-bed surface can be treated with a rubberized undercoating.

Chassis under the truck bed treated with 3M rubberized undercoating