Marshall, good to see you posting. I've got some more parts coming out of the Sovereign
today--the dinning table and maybe the storage bins and roller doors.
For you tire questin, see my thread on repairing banana skins. There is a photo and drawing in this post
which shows how the frame looks inside the belly skin. My Sovereign
has the spare tire carrier up front, with about half the tire showing below the skin. I think cutting a circular hole and slipping in a short cylinder of aluminum skin material, riveted to the belly panel, would provide adequate splash protection to the rest of the cavity. The cross member in the frame in my Caravel
has the bolt holes (threaded) for the aft end of the tire carrier trapeze. I would assume this is standard, even if the trailer didn't have the tire carrier option.
The drawing is a bottom view of how the tongue and main frame come together. You can see where the threaded attachment holes are and how the tire would fit.
During repairs, I partially filled the cavity with solid foam insulation, so the tire could go up tight against that--maybe put a sheet of skin material up against the foam for additional protection.