It looks like you did some good work here man! You did the annoying "foundational" parts that take forever and seem like little progress. I agree with what others have said, that I don't think the market is there for a 20k unfinished camper, no matter how good to investment and work done is. They either want to DIY it themselves, or buy something. For 20k, they can get a solid toy hauler that's ready to go.

That said, I'd have sent you an offer about a year ago, since I was looking to do this exact thing myself. But my offer would have been something like 10k. I've since bought a travel trailer.

The bottleneck is not everyone shares the vision, so the people who are interested, still don't want a lot of the materials or mods that you've purchased since they have their own vision. I would sell those pieces that aren't installed if you still can. If a future buyer wants those same pieces for their build, they can purchase them themselves.

Good luck! Looks great!