Does anyone have experience (good or bad) with contractors in the Tulsa who seal off crawlspaces and install dehumidifiers? Looking for recommendations or warnings.

Todd one straightforward strategy for addressing damp crawlspaces is to apply --closed cell-- (not open cell) spray foam to the entire underside of the flooring deck of the home, provided you have some sort of sheathing or substrate below the finished flooring. This creates a vapor barrier that prevents humidity and odor from entering the interior of the house.  

That said, persistent moisture in crawlspaces can affect foundation stability in some instances, in that case its usually better to address the moisture intrusion at the root cause ie, routing water around the perimeter of the home via french drain system. 

Hope this helps. Jose. 

Thank you @Jose Ruiz . I ended up closing a vent that was allowing water into the crawl space and putting a plastic barrier under the space.  Next time I will look into spraying closed cell foam.  Thanks again.

Todd happy to hear you found a simple solution to the issue. Jose.