You can sand to 400 and be done. My PPG supplier showed me two panels, one wet sanded to 600, then PPG epoxy sealer. The other one was dry sanded to 400 using the same sealer. Both were painted Sunburst Yellow. There was zero difference. The sealer is rated to seal 400 grit scratches. All of the paint I have put on so far has come out perfect doing that. I am not a real enthusiastic sander. I have prepped the entire truck with 80 grit first, then 220, then 400 inside and out all by hand. I am no expert either, I just rely on them.
