Assuming the campervan is steel, previously painted, clean, dry, sound and prepared as detailed in the Technical Data Sheet we can recommend Rust-Oleum Combicolor Original.

This is available in many RAL and BS colours in satin of gloss finish.

If there are any areas of bare steel  these should be primed with Rust-Oleum 3369/3380 CombiPrimer Anti-Corrosion prior to application.