Thanks everyone - I know it's it's a tough question, just wanted to get a ballpark.
FWIW it's a 2016 TT, so the 6gal water heater and fridge are new, but I guess they haven't exactly changed much in... forever.
I figured (from searching on here) that the AC heat coils won't do much, but it's so cheap it can't hurt, especially if it's only 55 degrees outside or something. Plus the TT is ducted, so if I leave the cube heater in the middle I'm hoping it will circulate the air nicely.
Matt - it does have the "taller" 40's in it, filled up when I purchased the trailer about a month ago, just trying to gauge how much I might have left. Sounds like I haven't done much to put a dent in it really. That's brutal that I'll blow through an entire tank in 3 days w/ furnace though!
I really don't think we will do much in the winter, maybe local horse events as a "base camp" for us and some of the riders to hang out during the day.