Diving into this project with a lot of help. If you are going to take on anything similar to my build I recommend both:
Build Your Own Overland Camper by Steve Wigglesworth pub 2016
Motorhome Self-Build and Optimization by Ulrich Dolde pub 2017
If you’re going to tackle a military vehicle I would also check out
Steel Soldiers Web Forum
There are a few folks out there that have had a vehicle built by a company or have built them on their own. I recommend checking these out for inspiration. I won’t get into sprinter vans, there is plenty of that stuff out there.