Hi, I have to have a fuel tank that measures about18" long, 7" high , and 18" wide, but figure I have to make it from .040 aluminum. Do you carry such a fuel tank that will work, or sheet aluminum about 48" x 36" ? If so, how much would they be?

You'd have to make it yourself with sheet aluminum and then weld it. Skycraft usually doesn't have fuel tanks, but a lot of aluminum.

First of all what is the tank going in? It really matters especially if you are installing it in a boat or an airplane or a race car

No fuel tanks at this time. Not normal for us. Yes, we do have a good selection of sheet aluminum; if you wish to construct one.