Here is what I would do.
1. Wash and scrub with dawn (if the bed has been used).
2. 180 or 220. Red scuff pad in the crevices.
3. Clean with SPI 700 or 710 or both if you think it needs it.
4 One more coat of epoxy to seal any rub through and to enhance adhesion.
5 Spray bed liner after at least a few hours, but not longer than a couple days.