[skyking]

Originally Posted by freebeard

So you're going to build a 5th wheel foamie to pull behind you '03 Beetle? That's awesome. I've seen Youtube videos of two custom 5th wheels that pivot in the center of an older Beetle (like the one from the 60s), but none on a New Beetle.

This 2" foam is going to be skinned with fiberglass isn't it? Maybe you could drill holes in the foam and put wood dowels or metal Z-straps in them to tie the two skins together.

Not a 5th wheel, a conventional trailer lower than the roof of the beetle. Looking for better mpg and multiple functions.
I had thoughts on tieing through with some twisted strips of saturated cloth, laying it flat on each side like a flower. It would be a 1/4" column of glass and epoxy through and then laid out in all directions. Labor intensive but strong.
The first thing is to build the foam bottom shell, cutting strips of foam and gluing together, fairing, shaping. Then I'd stop and make test pieces with various layers of cloth.
Test to destruction to see how much cloth can go on before it is a certain shear failure. See how strong that is and if it is enough, THEN order up the cloth and lay up the lower shell.
Stronger foams can support stronger layups. With a weaker shear modulus, there is no point in going past the limits except for making the floor surface more impact resistant. This yields a very light structure. My guess is no more than 6~10 oz cloth each side.
Ideal resin to cloth is 1:1 by weight, but real world is wetter at ~1.5:1
20 oz cloth plus 30 oz epoxy and fairing compounds plus 72 oz of EPS per square yard is close to 8 pounds.
The upper and lower shells of the small trailer are ~ 8 square yards each