There is no sub in the pics but I do have one. I think you are referring to the computer housing. The housing is made from plywood and sprayed in LineX the same as the dash. The front face is a brushed allum. plate and inside is the computer and a MTX amp.
The texture is actually very even and not ruff to the touch. The pics actually make it look rougher because the light is reflecting off it. The material is called LINEX and is a type of polyurethane spray bed liner.
Sorry to bring up an old post if it bothers anyone. But I've got a question for the Blazer owner, did you have to buy and install a high output alternator? I've got a sub and want to put a carputer in my Blazer but I'm trying to figure out if I'll need to fork out for the high output alternator.