I've welded in the seat rails and the underseal has burnt off underneath. Also where the floor was seam welded (by a blind monkey with a stick welder by the look of it!) by a previous owner the underseal has come off and it's gone rusty (surface). What's the best way to seal this? On the inside I have wire brushed down to bare metal and then sprayed etch primer on so far. Going to use primer filler and then top coat, and in the engine bay too. Underneath I was thinking at rubbing down, underseal, hammerite or stonechip. So far I've wire brushed the underneath, put some jenolite on to kill any bits of rust not brushed off and coated with a zinc based primer. I've pulled the underseal off where neccesary but not in the places it doesn't need to come off. I've seen this POR15 stuff too. Basically I don't want to the rust coming back. I hate bodywork/ paint with a passion but determined to do it myself All advice appreciated! what's the best way to treat it? I have a compressor and paint gun.