Here is a collection of helpful posts and personal notes on other cosmetic issues:
Finally, a topic I actually know something about! I've been doing paint work for many years.
Tom Henry had a pretty good article in Electronic Musician years ago that outlined his basic approach to painting. The process is actually pretty common-sense, and I've been using it for years (with a few modifications from the auto-painting industry).
1) Remove all contaminants like tape adhesive (from doing your panel markup) using your favorite solvent (e.g. MEK, lacquer thinner).
2) Do your surface prep. This is where everyone usually goes wrong. Chemically prepare the surface or sand it using progressively finer grits of sandpaper. I usually start with #80 and end at #220 with the primers I use (this is with an orbital sander). YMMV--some people insist on ending with #320. The chemical preps can be pretty nasty, especially for aluminum. One of them (from DuPont) is a chromate conversion step, which I really don't recommend due to its high toxicity. Instead, I suggest an etch primer (see step 4).
3) Vacuum off all sanding grit and clean again with solvent to remove any skin oils, etc.
4) Primer coat. Aluminum in particular is challenging to paint, at least if you want the paint to stick and take any abuse. I use a self-etching primer made by SEM. You should be able to get it at any auto paint store. Just stay away from some of the other products these stores carry, like the two-part urethanes (see next step).
5) Last step--the topcoat. I would bet that the paint already on your panels is a primer if it looks like a flat enamel, and it can probably be topcoated with just a little scuffing (wet-sand with #320). You can probably skip steps 1-4.
Most likely Polyfusion contracted out their paint work and an extremely tough industrial or auto paint was used, typically an epoxy or urethane. Unfortunately, the hardeners in these paints, particularly urethane, tend to be extremely toxic. People *have* died from being exposed to this stuff. Steer clear unless you have the safety equipment (a complete air-supplied suit). A charcoal-filter respirator is *not* good enough, no matter what anyone tells you. (I still can't believe so many auto paint stores recommend this stuff to anyone who walks in the door!). You probably won't ever be dealing with these paints as they require a spray gun, but I always warn people anyway.
What I find to be about 80% as good as industrial or auto paint is something you can find at any home store. It's the "Hammered Finish" made by Rust-Oleum, and it comes in a few colors. If you let it cure for a day or so and then bake it in an oven on the lowest setting (about 170 ºF) for an hour, it will become really hard and tough. Of course, this assumes you want a slightly textured-looking finish.
It's too bad there aren't better paints available to hobbyists these days. Most spray paints are total junk--you can scratch them with your fingernail. That is definitely *not* the case with the Rust-Oleum hammered finish. I remember there was a clearcoat years ago that was really great--a clear epoxy that came in a spray can. They must have put in some kind of inhibitor so that it wouldn't cure in the can. It evaporated when you painted and the epoxy then cured to a tile-like hardness. It was like auto paint without any of the safety issues. Naturally, they discontinued it.
There's another hammered paint I'm thinking of--I believe it's called "Hammerite". It's supposed to be pretty good, but it has a cure time of something like a week. That's because there's something in it that slowly cross-links the finish, making it really tough. I've never used it, though. I was kinda put off by the long cure time.