I keep a 500w blow heater on in van and its on a timer and stat which keeps damp out of woodwork etc,dont panic as only about 12 to 16 weeks and good weather will be back.
Non of there biz,i told some of mine years back when working on cars,that they only bought one house in street but if they wanted mine put a good offer in,im still here and some moved other shut up.
I did mine with bubble foil and 1 inch loft insulation over it,the foil alone is ment to be as good as 30mm insulation,the big w/screen is where heat and cold cause a problem.
Yes a wiring dia on basics part block units would help,say one for charging either from smart alt or old type to service batterys,then one on fused layout to usb plugs and lights, heaters toilet etc where folk could work on from to there own van requirements.
I love the big space in my van,i can carry six people if required,some times my kids want to take a friend out for a day with us and all there toys like bikes swimming gear etc.
My table clips onto wall bracket and the leg underneath folds down and clips to a we plastic joby on the floor,when not in use the table clips onto loo wall.
Yes these are best for conversion at about 25 to 27 ft long and some stuff already inside.
About 2 grand or less will have you a great van by miles topping at around 10.000 bucks,try buying a factory van for that,and it will be done your way.