The efoy looks a very nice system but for myself I don't think I could bring myself to use that due to the running cost of the fuel.
In summer I am confident my largish Solar + Battery system will provide everything I need power wise, using it for both refrigeration and cooking.
I designed my setup to use for primarily summer and some 3-season camping, and would think it would be ok for that still.
However in Winter, I can't see an all-electric setup being able to cope with a Wild Camping scenario if you were settled in one spot for say 3 or more days unless you had maybe 500Ah of USABLE battery power (I have 220Ah).
Should I be in that kind of situation, I will be fine for Fridge and the like for an extended period, but I would be using my little gas cartridge burner that I carry for outside use, than the Induction Hob for cooking/tea making.
Heating wise, diesel heater whenever I get round to installing it plus Electric Blanket just fitted this afternoon to try out potentially this weekend, but those gas burners put out a lot of heat anyway as a by-product, so using one of those winter could kill two birds with one stone (and talking of killing birds, window cracked open and roof fan on when in use of course!)
Camperbus Blog and Website - www.wildebus.com
Electrical Bits - stores.ebay.co.uk/Camper-Van-Kit