You might try removing one of the good bulbs and see if you can read the number. I went into the same problem when I needed to replace a bulb but couldn't tell what size. I called the service department after I couldn't find it in the paperwork. In my case it was a 921 bulb but I have a travel trailer.
Great choice for "Living within my means" and camping for one...
2011 Salem Cruise Lite 20RBXL & 2011 Toyota Tundra Dbl Cab
Camping History: 45 Trips / 133 Nights / 3736 Miles
FRF Social Group: Campers of the West