D/S= Drivers side? You didn't specify your coach model / year, so lots of assumptions here. Typically in a small unit, you will find electrical outlets only on one side. The GFI breaker is just that, it controls the GFIs in the bathroom, kitchen & exterior. Sounds like the "DS" breaker controls the other receptacles, and probably the 110V light(s) someone probably added, as 110V lights are a rarity. My guess is the 110V lights are the root cause here, either wired by amateur or something strange in the fixture / bulb.