We also have an Elkridge and we've spent up to a week in it during freezing conditions. Luckily plugged in, with an oil-filled radiator-style space heater going full time. The radiator kept the RV above 60F on low with temps in the 20's... and a stiff wind.... we had already winterized all the water lines, though. We were just using it as an extra bedroom during the holidays.
When it's ~40F outside, the furnace keeps us toasty warm, but it will burn through the propane pretty quick (and drain the battery, too, if you're not plugged in). I think it might be sized and insulated for maybe a week at those temps - using both tanks. Have you checked air flows at all the vents? There have been reports of some vents being blocked, or the duct work coming loose in the under-belly...
We have a "Mr heater" portable propane heater to augment the furnace during the day. It runs quieter than the furnace, too. It will run on low for about 4 hours on a small propane bottle.
I do agree with you on the SMALL oven. We use our oven ALL the time, and have plans to switch it out for the next larger size - it will fit in the same cut-out, but we'll lose the bottom "cabinet" (not that you can fit much in that, anyway). Not sure who thought that itty bitty oven was a good idea... they put the larger ones in most all the other model lines... (except where there's NO propane oven, which doesn't work for us).
Otherwise, our Elkridge has been great for us (knock on wood)... bought it new 5 years ago and have taken it all over the NW. We're based in the Seattle area and have taken it over to Boise, Salt Lake City and down the OR Coast almost into CA. Dave is very handy, so we take care of most all issues ourselves, just like we do in the S&B House.
Hopefully we'll see you at one of the rally's - that's a GREAT place to learn more about Heartland, customer service, and some of the tweaks we can do ourselves to make these units fit what we do as individuals.