I get the "project" thing. I've had several crazy projects myself over the years.
BUT, at this point, consider the GOOD and the BAD . . .
> You have a wimpy van chassis not a full frame like you thought. Adding several feet to the wheelbase will only make it long and wimpy.
> Everything is rotten.
> You have virtually nothing to work with. You may consider that a good thing, but if you at least had a solid coach, you would just be looking at a full interior redo which can definitely be a fun project.
You neighbor offered to buy it from you. This is a blessing from heaven - take it!
I really think Leadman had good advice. Find a solid coach, like his 80's Winnebago/Itasca Class A, maybe one that has a wasted interior. Gut it and make a cool updated interior that fits your needs. You'll be way ahead with a motorhome you'll enjoy.
1995 Coachmen Santara 360MB 36' w/slide.
Ford F53/460 chassis, 1997 Jeep Grand Cherokee "toad"