Either the Scott 3400 or the Alaskan Bushwheel API-3400 will do it, but you will probably need a spacer to get down to that diameter.
Be advised that these are heavy-duty items, and have proven very durable on Cessna 180s.
I have one on my Cessna 180 and the heat-treated steel tube tail spring has broken, but never the tailwheel assembly itself. The failures occur at the bolt hole in the tail spring for the tailwheel attach bolt. The latest update from Cessna that I had last time included a structural bond, which might help.
These tailwheel assemblies are probably overkill for RVs, but reliable and bombproof.