You need Propane gas for
You need Propane gas for winter (orange bottle).
Providing you have plenty of adequate insulation with some ventilation, that should be ok.
When you leave the van for a day or whatever in the winter, it’ll probably be bloody freezing when you return, so maybe a little truck cab heater may be an idea or something.
I would also want a “proper” toilet if I was living in it permanently as my home, as I sure wouldn’t want to take a dump outside in a snow storm! If you have a chemical toilet, you need to think where you are going to empty it.
HOWEVER, I’m sure there are some van “livers” who could enlighten more, as I’m just a leisure camper.