60 kwh at 4 kilowatt gives you 15 hours of heat in a van in cold weather. Granted, you may not need full 4 kilowatt of heat at all tines, so let's say it's one full day. You drive to BigSky Montana to ski and after two days your RV is frozen solid, including all the water and everything is dead and leaking. All you can do at this point is to try and find a shore hookup or an EV charger. But of course the batteries won't even charge because they are too cold.
Electric RV, you just can't, sorry.