For the mustang tank i built a frame for it to screw iton and then welded it to the actual frame w/ some tubing braces. these are the braces that go from the tank frame to the car frame. the angled part is welded on the sides and bottom, the top is not welded cause its the part that is gonna meet the tank frame, so its gonna be welded there. this is the done deal after a temp zinc coating to avoid rust as i work in the open. this should hold it there dont mean to show off my lessthan optimal skills, just thought it might come you handy.