Answer
For a fiberglass camper shell, scuff with 220 or 320, then refine with 400 or 600.
Why it happens
Fiberglass needs cleaning, dulling, and a scratch pattern fine enough for primer or paint.
Recommended grit
Use 220 or 320 for scuffing, then 400 or 600 for smoother paint prep.
Wet or dry
Dry for prep; wet can be used at finer stages where suitable.
Success check
The shell is clean, dull, and ready for coating.
What to do
- Wash the camper shell.
- Scuff with 220 or 320.
- Refine with 400 or 600.
- Remove dust before primer or paint.
Avoid: Do not use coarse grit as the final visible paint prep.