I agree with billlsbird . any welding should be done before painting.

and you cant beet the endurance of powdercoating.
much better than painting.

when I used to work for the local airport as a mech. we would use a product called LPS 3 heavy duty rust inhibitor in a aerosol can. on engine cylinder jugs right after machining to prevent rusting. it sticks to a vertical surface without running down to the floor and can be wiped off with thinner.