Shawn - I used so much painter's tape, it's not even funny. And I still managed to get some paint on the clear part. Oh well.
Holly & Jennifer - I would love to decorate guns with you! Anytime.
And yes, I used Krylon Plastic Paint - I didn't prime it at all.
So here's what I did:
First, you have to remove the stuff inside that the tape goes on. Tape up the clear part, if you don't want to paint that (some people do, I didn't) you can use tape or newspaper to cover it, and then tape around the edges inside and out. Tape the rollers and metal part at the end, and tape the trigger. The trigger is the hardest part to keep clean. I painted the inside with a sponge, spraying some paint into a bowl to get a layer down at first.
After that dries (1 hour with my paint, might want to give it longer), cover up the exposed posts and openings inside with tape - I used a bottlecap over the posts, and then taped around, and taped the other openings closed.
You can then take it outside and spray it - one side at a time. I advise lots of light coats, but you'll really want to hit that middle part with the Scotch logo, because you can see through the paint there unless you really drench it. After that dries, and you might want to give it a day, you can coat it with a clear sealer. Test it out on a really small area first though, because the first sealer I tried actually cracked all the paint and dissolved it, even taking some of the yellow off!
So I had to do the burgundy paint all over again, sanding down the bubbled parts with emery paper, which works really well if you mess up at all in your altering.
After letting that dry overnight, I used a rub-on that I bought at Absolutely Everything (Yes, this coming from the girl who hates rub-ons..

) and put it on the red part, going down the handle only a little bit. Then I sponged Mod Podge over it, in about 3 light coats over a half-hour or so. Then I added the stickers, Mod Podging below and above them so they stick better, hopefully.
Then I picked out my rhinestones, placed them, and used really strong glue (not sure of the type) to stick them down. And voila, there it is! I'm not sure what I want to do for the other side yet....