It sounds like you actually do have the winter package with heated tanks. I’d say, try it out and find where the red line is. This can only be done with experience, not hearsay. If you can get down to about 05 degrees F without freezing your valves and hoses, you’re home free.
the other option is to run the wheels off your propane tank and maybe even have a spare tank to swap in over a two week period. We just refilled our 575 gallon propane tank on the property @ $1.69 per gallon, so it’s cheap enough to use. Another option is a catalytic heater in the box, but I’ve not had good luck with those in the past because of the exhaust smell.
This should be a fine adventure.
We found the lower limit in N. Nevada in January. Even running the propane heater at about 55 degrees, cycling on every 5 minutes or so with the lower cabinet door ajar, the dump valves froze @ 12 degrees. So, above that number is our personal lower limit.
With your setup, it may be lower. Experience will tell. The actual water pump is vulnerable to early freeze up unless the water fill valve box is well insulated.
2020 Ford F-350 XLT FX4 4WD SRW SB SC 7.3L Godzilla Gas TorqShift 10R140 397 amps dual Alt dual batts Frnt Dana 60; Rr Dana M275 E-locker 4.30's 4580/4320/4066# payload 7243# curb wt. 11,300# GVWR 5-er prepped. 2020 Northstar Laredo SC, 12v compressor fridge, cassette, 320w Solar sub zero insulation.