The pre-dimpled 40-year-old liners in my trailer might consider 1/16" extra-soft foam tape an elective surgical facelift.
The 'pull' clamping force of a 1/8" rivet is minimal, yet is additive to the physical force of the gorilla pressing the rivet/sheet assembly home. Thus a 2-4psi force for 25% compression over a birdseye circle around each rivet (not much more to collapse the foam completely) will, with a (my) nearly disposable trailer project, not be a problem in this instance. Let's insert the standard disclaimer 'not recommended for anyone else' certainly.
No need to mask off the rib face - who is gonna see the overspray? The work will be preparing the aluminum so something will permanently bind to it, it takes chemically bonding a passive & inert layer between aluminum and your flavor of paint/sealer/adhesives to enjoin a lasting union. For your little-bit 26' trailer that's only about 425 linear feet or 28-30sqft of rib face to coddle...