Drywall Termites - What do I do?

[Jerald A Wilks]

Does anyone have experience dealing with these little creatures. I have a 21 unit apartment building in Florida and I have had four termite exterminators to it. All have found past evidence of Drywall termites (DWT). Two did not find any evidence of active DWTs but recommended tent fumigation. Two  observed evidence of active DWT and also recommend tent fumigation. All say that spot treatment works if you can identify the colonies. My understanding is it is very difficult to identify, and spot treat all colonies. 

I need to make a decision $20K for fumigation vs.$3K spot treatment

Does anyone have experience with DWTs and extermination companies that you can share?