Loctite sells a rust neutralizer primer. I have -zero- clue how well it works, but I wonder, assuming the rust isn't deep, and the rust is not near the valves or any necks (a weak spot there is not a good thing), maybe wire brush the worst of the existing stuff, add the primer, then spray paint after 24 hours, for a decent paint job.
I also recommend a propane wand as well. It won't tell you exactly where a leak it, but it will help find the general vicinity of one. When I check the LP gas lines of my TT, I use a wand and glycerin spray (soapy water, if not rinsed off causes corrosion), and when people ask what I'm doing, I tell them I am doing the Zippo test... needless to say, I get plenty of space to finish my work.