home again, home again, jogity jog. Here's what I have found out:
1) We drove home with the fridge on propane. When we arrived, the battery condition was just fine as measured by my volt meters, the go power controller, and the trailer gauge. all said that it was putting out 13.4 - 13.7 volts without being plugged into the Highlander. Brian, I re-read your posts about relying on the go-power measurement, etc. I don't have another way to measure the condition of the battery right now, but I am taking this as an indication that all was well.
2) I checked the 7 pin plug on the Highlander, and it is wired correctly. When the ignition is off, it doesn't put out any voltage. When the ignition is on, it measures 12+ volts. When the engine is running, it puts out 13 + volts. I take this as a good thing because my current assumption is I screwed up when turning the fridge on (which would have been Monday night), and that means that I didn't drain the Tow vehicle battery while it was hooked up Monday night / Tuesday morning.
3) As stated above, my current assumption (I think it is the only one that makes sense) is that I goofed when turning on the fridge to pre-cool it, and somehow set it to "DC" rather than "Auto" which is where we usually have it. That would explain why it was a little slow to cool on Monday night. I had been blaming that on the fact that I didn't have batteries for the little blue cube fan, but operating on DC makes more sense.
By the way, I paid about $450 to have the Highlander wired for the 7 pin Plug, and to purchase a Prodigy P2 brake controller. The old guy at the hitch place said there wasn't any functional difference between a P2 and a P3 unless I had hydraulic brakes in the trailer, and he wanted almost $100 more for the P3. Anyhow, I am happy with the P2. I miss the Sienna, but I think the Highlander does a better job of pulling the trailer.