Unfortunately Fish - I don't think people understand what you're asking.
Inner tube is used for when your tank repeatedly slips, or if you have problems with part of the bike burning holes through your tank. It goes between the tank and the frame.
I know what you're saying - you have to torque the bolts from the tank down so hard you're cracking the stud bolts that are welded to the tank and you don't want to use the brackets.
Try going to a machine shop. See what it'd cost to have some sheet metal brackets bent and drilled for the studs to make a custom fit to your frame. Shouldn't be much at all. Then, take sliced inner tube and put it between the tank and your frame so you have some compression room and a nonslick surface - but not so many layers that you're needing to overtighten the crap out of it.
And, as I said - get a luggage rack that goes over the back wheel. Get a drill bit, punch out 4 holes for your tank and put the tank on backwards so the petcock is pointed towards the motor. Ouila. Your tank is behind you and still above the carb for the gravity feed. Those luggage racks, if you don't have one, run 15-20 bucks at walmart, and the drilling is super easy.