If using the aftermarket trunk floor panels, I will tell you that the tank is no help in aligning them...I gave up and just used a square and a tape measure after hours of trying to use the tank...then just welded up and re-drilled the mounting holes for it after everything was square and sitting where it should have been.Clamp or screw your frame rail in place, then fit the floor section in. Once you have everything lined up put a couple of tack welds on the frame rail to hold it in place. Remove the trunk floor pieces and finish welding the frame rail. After that you should be good to weld in the trunk floor. Btw, use your gas tank to help with trunk panel fitment.