Hi Paul,
I know that some folks have used Outwater Plastics to source some of these materials in the past:
http://www.outwatercatalogs.com/
Hope all is well, I still want to come down and see your mods to your trailer, and have some margaritas. I took my '63 Overlander out to Lake Bastrop last weekend and had a great time.
-Marcus
On Edit: Heh... looks like Steve beat me to it.