Need a Tonneau Cover

Is this something to take off when towing? Or is this something to put in place when not towing? I like cross bed truck boxes, but I also wanted a hard cover and as you know they are really not available. What I did was get a short bed cover off craigs list and then cut to fit for the truck box. Ended up cutting about 8 inches off and I made some hinges to fit a piece of angle iron that I welded to fit across the bed and bolt to the truck box. Now I know you wont want to bolt to the tank but if you think you can make something fit that you will like. for the tank fueler you could get a long cover, as to cover the tank and hinge to raise for the rest of the bed. Make a cut out for the fuel port. Basically would be a 2 piece setup with the long one to be removed when towing?

Just a thought.