After enjoying about 20 minutes of cold food in the fridge and warm air from the furnace, both appliances decided to cease working during last weekend's festivities
A quick bit of troubleshooting revealed that while the fuses were all good and I was in fact sending the appropriate 12v throughout the coach, there was apparently a wayward "junction" somewhere... We transferred the grub to Boy Scout's outfit and bundled up with extra blankets inside and had an otherwise fine weekend. After work this afternoon, I tore apart literally EVERY opening inside the motorhome, tracing the 12v wiring from the fuse block to the offending appliances. Roughly 45 minutes into the good times, I came across a bundle of wires draped over a section of air duct, that when wiggled just right, would fire up the fridge and furnace 
A little tugging on them brought them up to eye level (although I was laying upside down and sideways on the floor, peering through an access hole about *this* big). What I found was 3 wires loosely embedded in a wire nut... After reworking the offending wire nut, we have steady power where it should be 
So the lesson here is, if you for some reason must us wire nuts in an automotive application, at least give it a good wrap of electrical tape around the bundle to help prevent the otherwise inevitable vibration-related loosening of the connection.
