I don't think coroplast would hold up very well on the front of the trailer, where it's exposed to flying debris and such. I may also be wrong there.
I'm guessing the fiberglass maybe just be a thin sheet of Filon or something similar on a piece of plywood. You could put lots of thin sheet goods over that plywood, if that's indeed the construction. Sheet metal, such as diamondplate aluminum, would last a long time. Countertop laminate (the thin sheets for gluing onto surfaces, not the preassembled countertops with particle board substrates) might also work well.