Sand with 180 grit without burning through it anywhere you will be applying body filler.
Move up to 320 grit before final coat of epoxy primer (if you are staying with epoxy primer as the final finish).
Epoxy primer acts like filler primer when you sand it, except that it is harder. It feathers nicely in my experience.
Last edited by 52Carl; 04/09/2019 1:28 AM.