It has been amazing & maintenance free.I recently went to a trade show & they had several booths with much the same product we used so its getting popular & some of them are now applied/sprayed on as a 2-3inch thick walk-on insulating foam impervious to moisture.

Yeah, I’m a fan of the old folk...they’re gentle on rentals for the most part vs the younger renters.  

We've brought in two dehumidifiers which are helping, but I'm not sure what the root problem is or even who to ask for help.One contractor said moisture is coming through a hole in the exterior stucco, but another said no way because the vapor barrier would block it. 1st one recommended installing insulation, but I've also read this can increase condensation problems.

Tenant agrees to allow Landlord timely access to premises to do maintenance and repair.Tenant will notify Landlord in a timely manner of any damages or problems as they arise, including damages caused by Tenant, malfunction of appliances or fixtures, and water/moisture leaks and spots.Tenant will take care of the premises, keeping them clean and clear of debris.

I'm not their social worker as sorry as I may be that they can't seem to pay their bills.At any rate, pretending to be the property manager may be a more "gentle" way for you if you just can't say "this is the criteria I must legally follow for every person that contacts me regarding this rental property".Gail

Dry all studs and sheathing to 12% moisture (some contractor’s use 15%).

Here is the link:https://www.epa.gov/mold/printable-version-brief-g...It's a good read, whether or not there is the potential for lead based paint to be disturbed.Another booklet about "Mold, Moisture and Your Home" is also an essential communication that every landlord should be giving to every tenant.

If the existing floor is vinyl, the answer should be yes, you can because vinyl provides a good moisture seal. 

With the sun beating down on roofs year round, or leaves falling and sitting there causing moisture to go under the roof and rot wood, the usefulness of shingle roofs is not a lot over 10 years.  

Also, consider whether moisture is really an issue though.