Wow, that is a chunk of foam. My car has a full size spare and there wouldn't be room for anything like that. Just out of curiosity, how big is that thing? There is a local place that makes foam(also insulation for the space shuttle), but they don't regularly make high density foam like that, just mattress/car seat kinda stuff. I think what you'd want would be close cell foam. It is usually very firm and wouldn't absorb water. It that block is as thick as it looks, I can see making a tool box(like German cars) with foam on top and bottom, little water fall emblem in the center. That would be kewl.
Jack Byrd