Clean to bare metal and use weld through primer anywhere you need to be spot welding. I wouldn’t POR15 anything until the welding was done or I was at least a few inches away from where I was going to be welding, that stuff welds like crap.
Also remember that POR-15 is designed to go over cleaned rusted metal. It is not designed to go over sand blasted metal. To clean up bare metal in your
welding areas I use the 3M black paint buster discs. They are 4" in dia. with a hole and use a metal arbor. They also make a rolok style, but I hate those as
they always break. These 3M discs are pricey but they work very well. If you use the paint buster discs wear eye protection. They can throw some sparks and
the material from the disc can go flying as well.
