What if you'd rather just buy a van? We talk about the realities, some of them harsh. We'll also review the Stanley Cook Kit (it's great!), talk about how to screw properly (really) and I'll tell the tale of what it's like on our Interstates now that COVID-19 is firmly with us.
They're expensive.
RV Trader is a great place to start, to get an idea of prices, etc.
Conversion Trader is focussed specifically on self-built vans.
Don't just screw willy nilly into your van. Every hole is a potential problem, and it's a good idea to know how your drill works as well.