I apologize for the long lapse in progress, but I finally have an update. Today I finished the first round of sanding the outside surface of the camper shell. Then I made some filler putty with epoxy and saw dust from the orbital sander.
And then I applied the first round of said epoxy filler to the shell, filling the gaps and nail holes.
After this dries, I will sand down the surface and potentially do another round of filler. If it is good enough for government work as they say, I will probably flip the shell over and sand down the inside surface.