Robert, check out the following website. The VA has already conceded to using AO at Takhli. The site containst the following verbage;

"U.S. Air Force Veterans who served on Royal Thai Air Force (RTAF) bases at U-Tapao, Ubon, Nakhon Phanom, Udorn, Takhli, Korat, and Don Muang, near the air base perimeter anytime between February 28, 1961 and May 7, 1975."

http://www.publichealth.va.gov/exposures/agentorange/thailand.asp

You don't have to prove the use of but do need to prove that you were in the area. The VA conceded my exposure due to my duties as a Security Policeman that worked the parimeter.

You need to address this section of the attached:

"To receive benefits for diseases associated with herbicide exposure, these Veterans must show on a factual basis that they were exposed to herbicides during their service as shown by evidence of daily work duties, performance evaluation reports, or other credible evidence."

If you still have contact with one of your Supervisors, perhaps he can provide a "buddy letter" that will confirm your work area was close to the parimeter of the base where AO was used.

Good Luck
Steve