OP,
Could be a good idea to disconnect from shore tie, turn inverter off if you have one, and then see if the wiring is tight on the back of that first breaker.
Still,
Bobbo very likely has the answer, GFI right at the entrance. Some of those WinTasca's had a countertop extension allowing use of the doorway as kitchen surface. They might've stuck an outlet down in the entry to allow an appliance on that extension.
Dusty,
"The Topele 20-Amp Weather-Resistant (WR) GFCI is UL Listed to Comply with The NEC Code Which Mandates All Receptacles Exposed to The Elements to Carry a 'Weather-Resistant' Rating. Built with UV Stabilized Engineering Thermoplastic for High Cold Impact Resistance, The WR GFCI Devices Feature Stainless Steel Straps and Mounting Screws, As Well As a Conformally Coated PC Board to Protect Critical Components From Moisture. This GFCI is Ideal for Exterior Use and Covers Must Be Used with WR GFCI Receptacles In Exterior Locations Per The NEC Code. The Device Combines Professional Grade Lockout Action with The Slimmest Profile on The Market. The Topele Weather-Resistant Slim GFCI is Also Available In a Tamper-Resistant Model to Help Protect Children From Electrical Hazards In Homes and Childcare Facilities."
I like the idea of "slim profile" since it's really hard to install a GFCI, a Timer or the like in a box with downstream wiring, etc.
Funny sometimes, though, a seller will advertise something that's always standard as a feature. Like "Duplex" (aren't pretty much all outlets duplex?) or "three wire" (pretty hard to find two-wire) etc. So I wonder if the electronics in every GFCI aren't "conformally coated..."
So OP - Found that GFCI yet?