You could use sign vinyl. Add a little liquid dish soap to a spray bottle of water, spray the back of the tank, the front of the vinyl, remove the backing and spray the adhesive side as well. Position the vinyl of the back of the tank and smooth it out with a credit card. Make sure that you use plenty of water and you will be able to smooth the bubbles out with no problem. If you do get any, you can pop them with a pin or x-acto knife and work the water out of them which will allow them to lay down. Any small bubbles will go away after a few days.