We made this for some good friends who own a mobile food cart, Superfresh Carts. The letters where made of 100% caps then filled with spray foam for support.  We made each triangle individually then attached them to a strip of caps that served as the border.  We ripped a piece of thin plywood to add rigidity to the border.  The letters are attached to hardware cloth, which covers the entire area.

These are letters I made for Superfresh's new cart.