Weight will be a MAJOR factor in your build. Weight distribution and placement will also be a factor. House batteries, water storage, tools, cooler. For example I mounted my house batteries and water tank in the cabin above my rear axil. I cringe when I see some of the 4x4s with roof racks loaded to the max swaying back and forth. Spare tire, water, fuel, camping gear, you name it. This throws the geometry of the vehicle off and is a big issue with the handling and safety of the vehicle. Plus loss of mileage due to wind resistance.
Another thing we learned along the way is pack light, think just like backpacking. If you don’t need it don’t take it. We learned this on our first trip to Co. I packed everything I could imagine that I would possibly need on our epic journey. After several white knuckle adventures like Slumgullion Pass with the truck in Low1, tapping the brakes and the distinct smell of other vehicles brakes burning up then struggling up the next Mtn. was not fun. When we got back I went through the van from one end to the other, if we didn’t use it, with the exception of emergency gear it stays at home. The gear requirements are fluid and change with the type and location of each trip.
I did my first camper/van build in 1978! New Chevy G20 with options……$4500. Through the years figured out what works and what dosent. Present van is best so far ultimate in comfort, practically, technology. All the comforts of home with an ever changing view. The best part we saved thousands building it myself. I have a background in electronics/electrical so if any of you do it your selfers need advice give me a shout, I will be glad to help.