I installed Diamond Plate in the engine compartment of my boat recently. I used 1/8" aluminum, its actually pretty stout stuff and will work unless its unsupported. If its going to be unsupported (ie: plywood or liner underneath) you'll need 3/16" or 1/4" stuff. Most sheet metal shops have it. I just made a couple of templates out of thick construction paper (red rosin paper) and indicated where the bends were going to be and they cut it to size and made the exact bends. It turned out great.
Here is a post I made earlier showing a picture how it turned out.