Questions for the painters...

I add reducer to my epoxy primer, as recommended to be my sealer, then it is top coated. BUT that is on OUTSIDE of car I no doubt use a high filler urethane sanding primer before the reduced epoxy sealer, and then topcoat. \
Spot welds, sounds like smoothing it with a 80 grit flap disc, Then sand the area smooth enough with maybe 180? Then epoxy and shoot. It is the underside and truck floor right!????