I worked with a guy who used to put his rendition of Niagra Falls (American & Canadian!) in primer & clear coat. His metal skills were marginal at best. But boy could he sling some mud! He could probably build a car completely out of mud, park it next to the real thing, & I'd defy anyone to tell the difference! He's actually had a couple cars in major auto rags. One was a Nova in some Super Chevy, another was a GTO in Hot Rod, or one of those. He felt that you could sand runs out easier than scuffing & squirting over "dry" spots. He literally used 1/2 of a quart of primer on a guitar body. No neck, all interior surfaces masked off. Just a small solid body guitar. It took me 6 hrs to get the primer sanded down. So I know what you mean about someone who should never hold a spray gun in his hand! I use HVLP SATA guns for everything but primer. I use Nesco genuine/imitation SATA guns for primer. After I sanded that guitar body down, I re-primed it with 3oz.'s of primer! The most successful method of rust conversion is R/R. Por15 works well on rusted metal, as stated above. But you can literally hook an edge with a blade & peel it right off of clean, bare metal. I found that using their etch makes no difference whatsoever. The thing it adheres to best, is your skin if you don't take it off when wet! I can't work consistently with my screwed up back. Sometime's I bend over, or squat one time, & I'm done for the day, or week, or longer. If I ever get this thing straightened out....... I'd love to say I could get a halfway decent paint job on one of the Imp.'s before the Nat.'s, but I still don't have that kind of access to a garage full-time like that. Like Latka (Taxi) used to say, "If it one thing, it's always another!"
I have a pretty ok HVLP gun. It was the best one Home Depot had for $69.99 about 10 years ago. It's done pretty good for what I've used it for. which isn't a whole lot. I abused it a bit by thinning down some truck bed liner with Lac-Cryl 45 and spraying in to the fiberglass topper of my Bronco. It was originally green, but faded to almost teal. Now it's flat black, and looks much better. I always make sure to clean it out, and spray clean thinner through it until it comes out clear.
Do you have a link for that R/R stuff? All I could find was rust remover http://www.indiamart.com/neelamct/rust-removers.html I think I saw something like "Coroseal" by the gallon at HD, for like $22. I was considering picking some up to try out, then sand it down, and put some high build primer on it.