You can always try to sell the van. Back in the 70's, I bought a brand new Chevy 3/4 ton van. Long wheel base, no side window, back windows, 350 V8, automatic. Paid $5180 for it. I was into custom vans and built it into a somewhat practical van for weekend "truck ins" and somewhat custom with molded in flares, big wheels/tires, complete interior including refrigerator, bed, drawers built in, all the audio etc. When I decided to go back to college, one of the locals knew all about my build and what I put into it. He bought it for $8500. So the lesson is that indeed, you might get back something of what you put into your build. Only time, marketing and a buyer looking for exactly what you have and most importantly, the competition and what they cost will tell.
I do like your idea of trading towards a house. As a seller, I'd have the deal written up as 2 separate deals. The house at a discounted amount and the vehicle as a discounted amount. Why? Well, then the commission is less and a loan on the vehicle if they wanted to take it out would work. You'd need the 2 linked such that either both deals close or neither does.