Highly water resistent bottom

Interesting problem, perhaps solved.  I was excited when my neighbor suggested using Thermo Ply as a light weight, water resistant panel which will face the road.  Then he suggested painting a truck liner to really make the bottom durable.  So, last weekend we attached the thermal ply to the bottom of the floor, taped the seams with Gorilla tape and then sealed it with two coats of xxx

Then we used Thermo ply to build the water-resistant sides.