So the Kei Van models have the same chassis as they kei truck. The Mitsubishi Minicab and Bravo van have a 4cylinder option, I think the Bravo van is more common though.
Japan has a ton of companies that build campers out of kei trucks: https://youtu.be/tAOttYejUgc, https://youtu.be/w2MFziDLDLM
The Japanese also have a scene for custom campers: https://youtu.be/PCchHwJj00Q
I just have trouble finding parts, the websites I've seen either don't have them or aren't specific on the compatibility.
While they are old....they are low miles. Thats why I'm considering it. People here want $20k for their 20 year old truck with 200k miles. I would be more comfortable with a kei truck with 30-50k miles. I also think it would be easy to get views on youtube if I decided to go that route. I would definitely bed line the under body and paint over everything to make sure nothing rusts. Maybe I should find a Suzuki Aero powertrain and swap it....