tough decision dogdude. I have a short bed too. I have a 100 gallon tank that I took out of my old truck when I traded it. It was a long bed. Now I have a roll top cover and a fifth wheel hitch. It would take a months pay to fill up the tank so I think I am going to sell it and buy about a 40 gallon that is L shaped that can slide under the roll top and give me more range when towing my 5th wheel
Good luck with your decision.