You may have missed my other post, LVJJJ, but just to clarify I did not actually spank my son (and certainly not his friend!) I was joking. 11 is a bit old for that. I did have him sit outside the trailer for a few minutes, because he should have known better. That bed was already made for the night, and he knows he should not have been on it especially with shoes. No fun to climb into a dirty bed, so that is the rule.
I am a very mellow guy, and fully understand that it is not worth ruining a trip to go ballistic or anything. That is why my son's friend's parents never found out there was any trouble, because they would have felt bad and nothing they could do to fix anything anyway, so what would have been the point of that? However, we do have a small number of rules to follow while camping, just for safety and sanity. I don't think shrugging off damage caused by carelessness will do anything except possibly increase damage producing incidents, because then there is no consequence for poor judgment in a situation where he should have known better. He knew he blew it because he initially tried to cover it up with a pillow.
We all had fun that weekend overall, but this should have been avoided if simple rules were followed. If this was something unforeseeable, of course there would be no punishment and we'd just chalk it up to a learning experience.
Your suggestion for the repair is a good one for most interior walls, but for this particular location anyone who sleeps there will have their head or face around that area so I have to be conscious of that.