Lots of great info on this so far.. thanx all
I can still say that fiberglass would be my first choice. I may still have to go with another option for the first batch, but I do think I will look to fiberglass after that.
As far as the UV goes I should have little to no UV exposure inside the GH as the coverings are supposed to block >80% of UV sources, then you also can figure in the water blocking most of the rest.
I have also considered many different types of coatings (Corian, Rhino Linings, Formica, polyester resins, epoxy coatings, and numerous others) and while most of them have the potential to work (Formica is the exception, and will delaminate under extreme pressure/expansion strain) they are just too expensive ($6-10 sq ft.) to consider at this point.
I have looked into a few of the "aquaculture safe" epoxy coatings and they do look promising in particular is P0nd Arm0r, flakecoat and the Sweetwater Epoxy, and all of them state that they are safe for potable water/livestock storage. I am trying to decide if that is enough though.
I will look into the fiberglass school as I think the Tech College nearby might teach that. Hearing what you all have said I will probably not try to make my own, unless I can get into a fiberglass class.
I am still going to investigate other options for the time being while I wait on responses from some.