Seam bubbling arises when oxidation occurs between
seals at joined body panels.  This process
destroys the metallic body to the extent that it
occurs. While it's occurring, the chemistry
produces "out gassing" which causes stretched
gasket and paint material, often observable as
bubbles.  One particularly nasty aspect of this
process is that the first rust produced then
absorbs moisture from available air because rust
is mildly deliquescent.  This makes the rusting
process self sustaining.  So the analogy to
biological cancer is rather apt.  Once it starts,
it tends to go to completion unless heroic efforts
are made.  If we could prevent any more water from
becoming available to the process, it would not
continue.  But once it's started, you already have
a seal breach, so it is slowly dying.  Casual
stop-gap measures can slow, but never arrest
continued development.
John