I can get by with just over a gallon but here in south Texas (the “Other” big state I’ve been told) 25F is a brutal freeze.
If you have washer-dryer connections be sure to address them and don’t forget the tanks, HW tank and P-traps. Ask yourself “where can I find water.”
You guys are so far north I’ll bet you can easily see Santa as he is climbing for altitude on his way to the lower 48.
If your local RV service folks are friendly (and competent) maybe you could ask what their punch list is.
2013 F-350 CC SB 2WD 6.7PS
2013 Eagle Premier 351 RLTS
-SOLD- 2012 X23B
-SOLD- 2003 Ford Expedition 5.4, Bilstein shocks