Well, did some more poking around.
The furnace is removable on its own. No issues with it at the moment and although I want to (and will) remove it to look at it at some point, no reason to do that now.
The fridge, that's another story. Called up Norcold and they said the recall had not been accomplished yet, so to schedule a time to get it done. Working on that part. All the recall does is add the high temperature sensor, but it's still got some value I suppose. So I'll try to get that taken care of.
Looking at the fridge, everything is still working and now having a better idea what to look for, I figured out a few things.
1) Overall, the system seems to be working ok, which makes sense given the fact that the thing cools. I can see sky when I look up into the cooling vent area so the vent for that heater works fine.
2) The burner can area for the propane side was full of little bits of rust from the burner tubes. This is inherently concerning. It also explains why the propane side was perhaps more finicky to light off. And it explains why I turned it on, heard the propane flow, but had it then throw the error code for no flow. I vacuumed that area out and the burner itself looks fine and produces a good flame now, seems like it works correctly.
Norcold confirmed this unit was produced in '99, making it the original to the RV. So really it's surprising in many ways that it's still working. I think that makes it an obvious candidate to replace in the not-too-distant future, the question is with what. Part of the problem here is not fully understanding our full use case.
Looking at load analysis, we currently have a battery bank that has around 450ah of capacity. Assuming we go to bed boondocking with no electrical power and want to keep the fridge and furnace going, the propane fridge only takes 250-500mA depending on where I look. If I switch it to a traditional freon cooling style it'll still be 12V, but it'll take 8A instead. That's a big jump. The furnace takes 11A while running according to its label.
So let's say we shut everything off, asleep for 10 hours. Obviously neither the fridge nor the furnace will be running non-stop during that time, the fridge does change that equation a good bit. Add some solar to the roof like I've been thinking about and that handles it during the day, but not at night. I think no matter how you look at it, if you're wanting to boondock without running the AC, it does make it more possible.
So, more thinking required...