OK, back to the RV today and checked the shower overhead. Turns out, it IS a light, takes 1/4 turn (kinda tight) to remove the globe, then a 1141 bulb was inside. Inspected the bulb, looked OK but it failed a continuity test, so I will need a replacement. When I do, I will be able to find which switch turns it on and off.
Oddly, Winnebago's Wiring Inst-Body, 12V side-wall drawing does not show the shower light, however, it is on the ceiling/roof drawing and is called out as a LSH-3 (LampSHower-3, the -3 is the style) which is shown on the electrical callouts as a shower dome light as grtharris outlined.
Thanks to all who responded, appreciate your help.