Does anyone know of a source either online or local to northeast Massachusetts for FLAT fiberglass panels or something
similar?

I'm building my own partially-enclosed trailer for windsurfing equipment and am looking for a good material to make the sides
of the box. Has to be zero-maintenance, tolerate a lot of water/moisture (including salt water), and be reasonably priced.
I figure 1/4-inch would be a good thickness although thinner might work.

Seems like corrugated panels are available everywhere but can't find flat ones!

Eric Law