We had the Heffalump for about 9 years and lived in it for about 5 of those.
The previous owner had lived in it full time for 18 years.
If you full time in one of these trucks speed becomes less of an issue than if you are doing 1 or 2 week trips. You will probably have to wrench a lot yourself...
The truck circuits are truck only. No webasto, radio,fridge electric clock🤣🤣🤣🤣🤣
The only draws on the truck batteries should be lights, heater fans, air con, starter, wipers, sensors(4X4 locks)
The only Camper connection to the truck electrical system is the connection to the B2B.
Solar,generator, house loads etc. all go through the house batteries. Even the 12v power supplies and the radio in the cab are supplies from the house batteries (probably the spot lights too)
There is a main battery shut off switch I never used but might be of use to save the batteries until you track this gremlin down.
When you face the battery box it is top right behind a stainless vanity cover. You have to turn it with a "key" probably hanging right there, basically any flat piece...
The engine crud in the coolant circuit argument is just a non starter. If you have that much crud you need to flush and replace your coolant! I do maybe see the point about the air in the high rad, but in 10 years in the vehicle it was a non issue. Safety factor, it is oxygen barrier pex rated...