like i said in my other thread, i didn't have any luck with cheap spray paint.
you can actually ignore the advice of "many light coats are better than few thick ones" because even if it runs, it's not a problem. you won't see any runs through the tank, and unless you sit around admiring the back of your tank, you'll never see the runs. save yourself some time and do 2 or 3 thick coats.
my best advice though is to buy some latex/acrylic enamel paint, some $0.15 sponge brushes, and just spread it on. it's a whole lot quicker, and a whole whole lot easier to remove. it literally just peels off if you wanna change colors. scraping off spray paint is a pita and the lungs. it's also more water resistant for those few drips of water you get onto the back.