Minor rust under paint

[birdshill123]

In my youth I was a manager of a Ziebart rust proofing shop. Took lots
of training on how and why you get rust. Have you tried to poke an awl
through the rust? If the metal is perforated then the rust is coming
from behind the body panel. To repair this properly the cancerous
portions have to be cut out and replaced. Any other method of repair
is temporary and a waste of time. If the bubbling is simply rust that
is between the paint and the body then you have no real problem. Most
rust comes from the inside of the body, especially in an RV.

Bruce 1988 FC35