make sure you really need it. doing it for ~3-4 years and i kept it very simple. i have
-a bed (80cm*200cm thick foam)
-a table/workbench
-a shelf
-foldable toilet-chair so i can poop into trashbags
-large bottle to pee in
-not a fridge but a box that can plug into 220v or 12v. this is plenty, a fridge would be such overkill for me…
-diesel heater
i most appreciate about mine that it does not look like a camper so when i make my 2-5 day trips in it and park it in a little village, people often assume that it is just somebody's construction vehicle, not my nice little cosy place to travel in.