RV Furance on Predator 3200 (4000)?

Best (IMO) is to have extra battery and 250+ watts of solar.
A couple extra propane bottles may help.

"electric power to the water line" What does that mean? Heat tape?

A good 12V DC supply and a propane.

Battery or shore power via converter supplies the 12V DC....although battery is limited cause furnace fan is a DC hog.

Propane.......depends on what you have
30# propane cylinder (7 + gallons) will last a while if moderately cold
IF temp in the minus category.....I had to refill a 30# every other day :E

Battery.. but since you've been here 12 years I suspect you know that.

Ken,

Assuming you have a standard RV furnace that runs on propane, it runs on 12 VDC from your battery.

So to run it for extended periods of time, you would need to run you generator to power your converter or charger to recharge the battery.

Yes, you could also use space heaters directly from the generator, but that would be trading propane consumption for much longer generator run time. You have to decide which way you want to go.

You will have to check you rig to see if the propane furnace heats the tanks/plumbing.