As mentioned up top, I talked with Winnebago yesterday and got some advice. I then went out to the RV and tried some stuff. Below is what I learned:
Fridge: The Winnebago rep thought it should be OK. I turned on the propane, set the fridge to run on propane (rather than the dual-fuel electricity/propane/fridge chooses option), and, after 24 hours, it's running fine. I'll let it run for a few days just to confirm, but the freezer's down to 15 degrees Fahrenheit, so it seems to be OK. Yay.
Boost relay: On the 2007 Navion (and, likely, other, similar Itascas), the relay, and some circuit breakers, are under an extension of the "house" floor than runs forward between the cab seats. The Winnebago rep said, "you just lift the carpet." It turns out that you lift a heavy flat metal cover, carpeted on the top, that's hinged on the passenger side, and there's a cover, held down with screws, over the relays (that's what it says on the cover, anyhow). That cover's toward the rear end of the extension; the circuit breakers are behind a cover that's down in a well in the front end (wow! Another weird storage spot!). There's no obvious handle; I started tugging on the carpet in random spots, and the cover hinged up.
It didn't occur to Winnebago, as far as I can see, to put any kind of catch to keep the cover up; so, if I need to work in that space, I'll need to come up with something to hold it up so it doesn't crush my fingers.
The relay (aka solenoid) comes out to a battery-cable-sized cable (that is, a heavy/large cable) that's held on the battery clamp with a nut. I've realized that I can test relay function by removing that cable from the battery clamp and testing for voltage with and without the boost relay (momentary) toggle switch activated. If I'm not getting voltage, I can then open the cover and explore further.
I generally do electrical fault tracing from the origin point to the end, but no reason I can't work backwards.
It's a small cover; I bet if I have to remove the relay/solenoid, I'll be exercising my 56+ years of mechanical skill and my 74+ years of learning curse words.
