If I cleaned thr galvanised zink layer around the hole for the plug weld (and spraid with weld through primer), would that be ok? I think I read somewhere that the reaction that takes place can speed up the rust process if using galv?? Any advise.
If you take off the galv from around the hole, say about the size of a 10p then plug weld, it will be fine. If anymore of the zinc boubles up give it a light rub with a flap disc then spray over with cold-galvanising spray rather than weldable primer.
It will rust quicker than if it wasnt touched, as the galv coating will now have a weak point.
If you spray it properly it should happily last a fair few years.