by daveesl77 » Wed Apr 29, 2015 2:06 pm
I am not quite sure what your question(s) is, but I think you are wondering why use the plywood? 1/4" is fine if doing a laminated wall structure. The epoxy goes over the ply to make it waterproof and tough. You can also make the ply very water resistant by using the polyurethane "mix" system - start with 75% mineral spirits:25% poly, then 50:50, then 25:75 and finally going to full strength poly. Most people also put polyurethane over their epoxy to act as a UV inhibitor layer. With all that said, you might want to consider doing the "poor man's fiberglass", using canvas/titebond2/paint. It is tough has hell, costs way less, is easy to do. It has also been around for hundreds of years (well not using titebond) for the decks of boats.
If you are looking at wanting to pull a trailer with an electric car you have to be very careful with both weight and windage. The bigger the trailer, the more resistance you will have. You could build a 500# trailer, but if it has a 6' high, flat face and back, then you are going to severely tax the little car.
dave