As the saying goes: One battery, one night ...
Some thoughts:
Alde is good. The Sweden/Norway travelers here swear by it.
A fuel cell is an expensive alternative to a generator.
Solar will probably have limitations in short, cloudy or even snowy winter days. It works great in summer.
More battery capacity will help, lithium batteries are lighter, have more capacity, and cost more.
Additional insulation in the camper will help, they all have room for improvement.
I am not sure if it is a good idea to let the camper cool down during the day. A lot of the energy saved is needed to bring the temperature back up.
Maybe someone with personal experience with your type of weather will chime in.
