Rustoleum on a clean frame shot through a gun or even poof cans turns out nice after it cures its VERY durable.I was going to have everything powdercoated until a buddys restored Chevelles powdercoating started to flake and peel.maybe prep done wrong i dont know,but ive use rustoleum many times with much luck.Sanding it off sucks it will gum up paper BAD.I use it on floorboards on trucks for extra corrosion protection,or on the insides of doors and hidden areas it makes a difference.

I've been using POR-15 for 4 years now. One of the big advantages besides the rust-prevention is its durability. Once it dries and cures you can take a hammer to it. They now have a semi-gloss black available. I'll be getting some at the swap meet next month. For a frame, I would figure a bit more than a pint. You also need the cleaner and the surface prep to do the job right, unless you sandblast the frame first. It can be sprayed, but you need NIOSH equipment (external air supply) or you will ruin your lungs.

To extend the storage life, keep it in the fridge. If I were doing a frame I and had it available locally I would buy a pint and then see how much more I needed after I ran out so I didn't buy too much.
http://www.por-15.com/

I had my 4x4 frame sandblasted and powder coated for approx $250 in CO. I used POR 15 on everything thing else....inner fender, firewall, axles, etc. I like both. The one thing that I see as a disadvantage to powder coating, is touching up. When powder coating, try to think of every possible detail so you don't have to sand off and try to touch up. Paint is difficult to match. POR 15 is difficult to remove from you, or other items that it wasn't intended for. Powder coating comes in hundreds of colors! I would buy two quarts to paint a frame to be safe. My two cents