If so, you may want to consider installing a vapor barrier, but this could get a little pricey.

Technically you should use a product such as stego mastic then cover it with stego wrap (a vapor barrier plastic sheeting that is basically rip proof) This must be from the top to the bottom and it will not be cheap.

What about the vapor barrier

We recently had similar situation with our grandmother, at first she was complaining about inner ear pain, than she was loosing her balance and it did fall couple times.

You must ventilate otherwise you will condensate water vapors in this space. 

This will give you a vapor barrier under the floor. 

Plastic vapor barrier?

That is sealing off all vents with gasketed vent covers,  encapsulating dirt crawl space with 20 mil vapor barrier, sump pump, dehumidifier, airtight crawl space door, etc. 

.- Asphalt Roofing Manufacturer's Association "strongly advises caution when considering the application of any type of field applied coating over installed asphalt shingles," due to possible shingle curling/warping and possible vapor barrier may cause premature failure of roof decking.- Some shingle manufacturer's specifically state that coating will void the warranty.  

The banking industry and wall street created "VAPOR PAPER" that had no intrinsic value.