Rosemary and I painted the back of her FO 55 last week.
Thankfully, we initially set up the aquarium with enough space so that we could get behind it.
The majority of the work is the tape-and-newspaper stuff. No way we would spray paint in the house, so we used a can of black paint.
I realized that it won't matter if you decide to go with gloss or matte finish, because you'll be looking at the "inside" of the paint through the glass.
We used a sponge roller, but it took several coats that way. I think it would have worked better with a traditional 3' or 4' width paintbrush.
Lay it on thick.
Another lesson learned- be easy on any "seams" where glass meets plastic. Since the silicone isn't applied in a perfect straight line, a little bit of paint might get in those seams. It's not very noticeable in my case, but something to watch out for. Just don't wedge your paintbrush into the corners too much.