I usually pop over to the Moab or Blanding area several times in March/April/May every year. By March the weather has changed to "Variable" to say the least. We've encountered snow/rain and sunny low 60s all in the same day.
(1)Lows are usually in the 32-39ºF range and both the motor home and truck camper stay tosty warm with just the on-board furnace. Having a warm comforter allows you to drop the cabin temperature a bit to save on the furnace running the battery/batteries down.
(2) No generator at night, not allowed in campgrounds and a good way to get a knock on the door late at night from annoyed neighbors when boondocking.
(3) Solar panels are great for keeping battery banks charged without using a generator but I've never seen a solar array/battery bank large enough to run electric heat (very high current draw) at night.
Sorry no experience with rentals.
Welcome to our corner of the world, you'll love it.
Dave