What is the spray paint of choice for "field touch-ups"  

If one doesn't have an oven (or a big enough oven) to bake on a finish,  what is the recommended air-dry finish for a BARREL?

I have seen a lot of images of guns over in the sandbox that have been "tanned" with rustoleum.   I suppose the advantage is that if it wears or scratches - it is easily re-coated.  

Are there other alternatives (besides professional finishing of course)


Thanks!