Wall bubbling/ceiling marks/sources, severity?

OK, when I go in December to check out my prospective 1991 M26 I think I know what to look for regarding the exterior wood issue thanks to your comments.

Here are a couple more issues (my wife saw the unit last month, I was not along)

She said one spot in the wall had a small area of peculiar bubbling, like the interior had puckered away from what was underneath.  Reading over some old posts here I saw a couple along the same lines.

Is this something to worry about?  How would one fix such a thing if one could?  What causes it?  Etc.

One other thing the Mrs. said she saw, was the spot of the rear ceiling where one clamshell must rest on another, she said she saw some pretty obvious wear patches from the shells rubbing together.

Again, is this a big deal or no big deal?  Anything to be done about it?

Thanks again.  The more I think about it the chance to get a trailer this light and roomy for $7,600-$8,000 is pretty sweet.

I just want some confidence it will still be great for years to come, a 1991 is pretty old.