Well Sugar Honey Iced Tea.... Found a little more than I bargained for.
The instructions say you can leave the aux feed hose on with a tank attached, and when 'BRIEFLY' disconnected to change tanks.
'Briefly' because the male POL fitting does not seal.

It hisses gas. Gonna need a valve on there. For now the line is stowed away, and the stock plug put on. I really want to leave that line on, so I have one less thing stowed 'elsewhere', needing tools to install/remove it.
I did add a street 90 on the end of the regulator to reduce the curve in the discharge line. It was too sharp for my liking.
Used 3/8" Flare cap and plug to disconnect and seal the furnace line. Zip tied the disconnected line. After doing so, went around with Dawn dishsoap and water in a spray bottle to check for leaks.

I found them. The new cap needed thread sealant before it would seal 'bubble tight'.

THE THREE CONNECTORS LEFT UNDERNEATH - FRIDGE, WATER HEATER AND STOVE ALL WERE LEAKING.

From the 'main distribution pipe' fittings where they had the flare fiiting to go to 3/8 copper line.
I had not touched any of these, and I suspect they have been leaking since my owning the camper. Gave them all a 1/3 - 3/4 (!) turn and things sealed up. Not sure if it was an original assembly fault, or loosened up over time (?!?) .
After finding that, i went to every single fitting and checked. The end at each appliance was leak free.

Unnerving to find the leaks underneath, however. Should you be creeping around under your rig, bring a soapy water spray and pressurize the LP system. Might be surprised!! I sure was.
With the furnace disconnected, the LP smell on the drivers side is gone.