I'm really surprised at the responses. We do this all the time with night time temps in the 40s and the thermostat set at 67 or 70. We also don't have any LED lights yet but they are on the list. The only time we had a problem was when our 7 and 8 yr old batteries were going bad. We replaced them with Walmart group 29 batteries and have been going good ever since. We do have hook ups for solar panels from Harbor Freight so we can throw a panel in the front window at the storage lot or on the roof in a camp ground but don't always do it. We easily go 3 nights of full furnace usage.
We also have the foil insulation that we have cut to cover all the windows, exterior roof vents, shower dome etc. We mount these with friction fit or velcro. They are great for keeping heat in at night or keeping heat out and the cool in when the weather is hot.
Our propane tank routinely lasts an entire summer and covers all our trips. Most require heat all night long because we go to the mountains alot. We have never run out with only needing to fill it once per year.
Here is my blog post covering when we replaced our batteries and the decisions we made vs. the common wisdom on the forums.
A battery replacing we will go.