I used flat black spray paint and taped off the trim and sides. I just put a sheet down and sprayed mine in the house. I did it in the middle of the night so the wife wouldn't find out, lol. The fumes woke her up anyway. Boy, was she mad.
***EDITED TO ADD***
After you think you're done painting, get a bright light and shine it from behind the tank and look at it from the front. This will allow you to see any holes or spots that you missed. Just hit those light spots again. Once you get water in the tank, I don't think there's any way you won't like it.
Roll on Latex paint is super easy to remove, but it really hard to get it on. You have to do a lot of light coats, while letting the previous coats dry.
I've heard that spray on paint (spray can) is harder to remove. But if I have known how hard the latex paint was to use, I would have used spray paint.