That gave me another idea. as long as your not using the product to actually hold water like a plywood tank, but rather just waterproof the bottom, truck bed liner paint should fit the bill.I could maybe make a fastening system like they use on pick up truck covers.
http://www.summitracing.com/parts/rl...FWRp7Aod2hoANA
http://www.autozone.com/paint-and-bo...ing/98214_0_0/
http://www.autozone.com/paint-and-bo...ing/69491_0_0/