Rustoleum makes a spray-on rubbery coating and there's also a company that makes a product called "Plastidip", which I believe is a similar thing. I used the Rustoleum product in black. At first I freaked out because it was really liquidy, but you have to have short, even strokes with it and eventually it covers really well. One can took care of the back of my 40-gallon. And it will peel off later if you need to make a change. It's got a smooth, matte finish.
If you look in the spray can aisle at the hardware store, it should be easy to find. Sorry I didn't remember the name.