Re: "Rubberize" base of Propane tank(s)?
The problem with applying coatings is what may be happening UNDER the coating. In order to avoid that, I'd suggest just cleaning the tank, applying a couple of coats of a durable paint, and then placing a rubber pad in the storage compartment to prevent any more wear.
With a 20# tank (which seems to be 17# under the new math) you are likely to be swapping it out, not refilling it, at some point. Which also means you won't have to pay for tank inspections. Better to leave them naked, or add some more plain white paint, and avoid issues there too.