What thickness of Coroplast for enclosing TT underside?

When I worked on our trailer last year I found that the cheapest place to buy Coroplast was from a sign shop. Prices varied widely, but I was able to get it for about $15 for a 4 x 8 sheet of black Coroplast. The thickness was 1/8". I glued foamboard to the decking above for insulation. I also had to add some crosspieces to have something to screw the Coroplast to. I used 1"x3" lumber for this.