Yeah, what he said. I recall that when I painted my aluminum garage door there was a product that I used to clean the door with first (not TSP, but a clear liquid) then a specialized primer for that type of thing. Go to a good paint store (not Home Depot) and get advice and the products from them, or get it powder coated (not sure where you'd do that, though).
If you want to get fancy you could use a very thin-walled section of aluminum or perhaps even softwood and then give it a thin coat of epoxy and wrap it in a very light cloth of fibreglass or spectra or something like that. Even hemp, if your into that. Polyester resin will not bond well to aluminum, but epoxy will bond really well, and adjusts to temperature the same as aluminum also I think, and it will seal wood and absorb in about 1/8". Use some very fine wet-dry sandpaper to scuff up critical joints before you epoxy it. Of course you can buy carbon-fibre tubes now in many sizes. I think it would be neat to make a pack-frame out of bone dry spruce or cedar branches sealed with epoxy, maybe fastened together with whipping twine sealed with epoxy. Wouldn't be all that much heavier than aluminum when done, and it might look way cool espcially if it has natural curves and tapers. Wood and natural fibres are fairly competive strength and weight wise once they are dry and sealed, but I don't think any traditional natural resins are quite as good as epoxy though. Softwood and epoxy is a wicked combination.
ROTFLMAO <img src="/forums/images/graemlins/grin.gif" alt="" /> <img src="/forums/images/graemlins/grin.gif" alt="" /> <img src="/forums/images/graemlins/grin.gif" alt="" /> All paint is going to do on a pack frame is get scratched up, and dinged making your pack frame just dingy looking after a few trips <img src="/forums/images/graemlins/smirk.gif" alt="" />
PEPPER SPRAY AIN'T BRAINS IN A CAN!
Aluminum won't rust, and the paint will add unnecessary weight. Entering a beauty contest are you? <img src="/forums/images/graemlins/smile.gif" alt="" />
Actually aluminum DOES rust, it just takes 20 years. We had some collapsible aluminum tent poles which, after about 20 years, got bubbly white spots on them and the surface got more rough. We actually had to sand them down once to make them work as the aluminum oxide got in the way of the poles sliding.
It won't rust through but it does get surface oxides on it.