So you just mean not a heater, just the tank / calorifier / heat exchanger part of it.
Not much use for those camping days and weeks off grid without driving.
Do you have a lot of experience doing that? We live in the van so max time spent not driving is a weekend or so. Water stays hot for 24 hours in cold climates, longer in moderate.
Also, isotemp has 120 volt option to heat it too.
I can't tell you what the best option is for your case all I can do is advise what others have done.
If you have to have hot water there is isotemp, your Bosch water heater, Rixen system, solar heated PVC pipe on roof, propane or electrically powered tankless hot water heaters. Go research them and let us know what fits your needs. We can advise from there.