I have a 40-year-old motor home. The aluminum body is painted white and is starting to blister in some places. Do you have an undercoat paint for aluminum? I could seal it once I have removed the blisters. And can you recommend a top cost gloss paint for use with a roller?

Assuming the bare aluminium is clean, dry, sound and prepared you could consider Rust-Oleum 3302 CombiPrimer Adhesion Primer.

This can then be over painted with Rust-Oleum CombiColor Original.

This can be mixed to many RAL, NCS or BS colours in a satin or gloss finish.