Painting the background of a tank is the BEST background (maybe besides 3D backgrounds). It's certainly the easiest, cheapest.
Spray paint is the way to go. I've painted both my tanks, my FW
community is black and my SW FOWLR
is blue. I used Rustoleum Gloss on my FW
and Krylon Gloss on my SW
Comparing the 2 experiences, it was much easier and I had a better outcome when using the Rustoleum.