The standards for what should be in a report has changed-particularly on agency file reviews, historic USTs, vapor intrusion and even what constitutes a REC.

By remodeling every inch of it including new insulation in the crawl space and a vapor barrier.

A normal title company might vapor lock over a non standard deal like this, but your RE attorney can create all of the required paperwork to get this deal closed. 

I'd also add a vapor barrier to reduce humidity in the crawlspace. 

So, I have a somewhat working knowledge of physical plant issues (sagging roofline, foundation issues, vapor and moisture problems, etc.)

If one or more people are sleeping in the room then the problem is most-likely cause by the vapor the person(s) are breating.As mentioned in several posts, my company deals with your type of problem and most-often the problem is the result of the people breathing vapors when they sleep and lack of good air movement and ventilation in the room.

It's a grind and my savings is on vapors. 

Now my war chest is on vapors and I only have the "free" options for marketing now, and brokerages in my case say "just call people you know". 

If I just do no cell spray foam, will I create a vapor issue?

My guess is some work is going to vaporize in the next couple months after the time period for the PPP money ends in mid Oct. and some folks lose their jobs.