Over the course of a few evenings after work I started filling some of the holes and cracks on the inside of the camper with wood filler.
My helpers filled the knot holes in the walls and floor. After drying over night I used my belt sander and 120 grit sandpaper to go over the walls. The belt sander did really well and smoothed up the wood quite a bit. After everything was sanded and the dust cleaned up, we primed the interior walls with Kilz2. This primer covers well, I did 2 coats. It also doesn’t have the overpowering fumes of other primers.
After the paint dries I plan on getting the ply for the interior roof and installing it.