I went to ACE hardware and bought a couple of metal hose clamps and coupled them together as a strap around my tank. It hasn't slipped/rotated since. Below are a top and side view of it on my beach cruiser. the only thing is one side of the strap has execess on it that I will cut off. I figure it should work for most frames and it's adjustable. Now I don't even have the nuts/straps on the tank studs eliminating the potential of the tank stud snapping off and leaking fuel everywhere. Just thought I'd post this up for anyone having same problem. I know there's other posts on this but its just my two cents.
That's a good way to ruin the tank. Go to a tire repair center and see if they have some old tubes that they might give you and cut a good
length strip from one that will fit in the base of the tank. Then, buy a can of "Elmer's, Extra Strength) spray adhesive and spray the bottom
of the tank so you can place the rubber strip along the indention in the tank. You can buy the a strap that is used to hold duct work up in
furnace installations which have several holes in the strips. The coil of strips can be cut to length to fit the tanks' mounting studes. You
can also paint the strips to match the bike. All of this stuff won't cost you much and that tank will not move if you use the adhesive and
the straps to hold it. The spray adhesive is real tacky and stays that way plus it has considerable strenght that is water resistant. Ace
Hardware has all of this stuff and this will hold that tank better than the hose clamp and it can be a permanent mount for the tank.