I would suspect bulbs since inside and outside lights are not usually on the same circuit. RV wiring is, however, notoriously unpredictable. Two units of the same brand, manufactured on the same day may have completely different wiring setups. Depends on which plumber was stringing the wires.
A simple multimeter on 12volt probe light is your friend. Be sure you know which switch is "supposed" to control which light. Some interior lights have a secondary switch on the fixture.
Also, you cannot always find a blown automotive type fuse by looking. The best bet is to take a known good fuse and substitute it into each slot down the line. Like you look for a burned out Christmas tree light.
Good luck.