Where can a person order plastic that is strong and waterproof, yet easy to manipulate? Turn into shapes.?

Answer 1

Acrylic sheet (Plexiglas) can be formed and shaped after heating to about 230-250F in an oven, handled with gloves.
Acrylic sheet is available at most hardware stores as a window glass replacement. Thicker versions, rods and tubes, are available from Plastic Suppliers in the Yellow Pages.
Acrylic is moderately strong and definately water proof and can be "welded" with solvent.
http://www.sdplastics.com/acrylic.html