Thanks again for the great feedback. Hopefully this thread is useful for folks that end up encountering a similar problem. I ended up grinding down the head and mandrel with my rotary tool. Then used a chisel to cut off the remainder of the head. At that point I punched the body through.
I was kind of surprised to see so many of the nails poking out from the rivet. I would think that would be an exception to the rule but on my Scamp
it seems to happen with more than half of the exterior rivets.
This is my first time renovating a scamp
(or any trailer) so I'm sure this was just the first of many questions I'll have for the group.