When I replaced the rear bed on my Ford, I also dropped the front tank, since the straps were rusty.
It came from the factory with canvas sleeves on the straps. Which, of course held water and would hold road salt if we had any down here.
I did not like the shiny/rusty marks on the tank.
Where the straps were, was shiny from vibration, with rust on both sides from the worn off rust under the straps.
This is what rusts out crossbed tool boxes. The rubber between the rail and the box rubs all the paint and coating off the metal, it rusts when it sits still, then the rust gets rubbed off when you are moving again.
Eventually this eats through either the rail or the box.
I did the tank straps the same way I do the tool box, but did not use the thick rubber I use on tool boxes.
I went to the plumbing department at Lowes, and bought some bathtub pad material.
Its thick rubberlike material. Tough as all get out.
The secret, is to use two pieces. On the tool box, I glue one piece to the truck rail so it cannot move and abraid the rail.
Then I glue a second piece to the toolbox so it does not get worn either. Then, I put some grease between the two so that is the slip point. Plus there is little wear either because of the grease.
Unless you weld it, that toolbox is going to move slightly under heavy vibration, so I want it to slide rubber on rubber instead any metal getting involved.
I did the same thing with the gas tank.
Wrapped the rubber around the strap, very well glued. Then a strip on the tank with grease between the two.
In my case, it was almost too much. It wound up being thicker than stock, and the bolts were hard to start, but it worked.