If you're having trouble finding the components, ask one of the guys working in the shop at the base, some may be ex mechanics, at least they were at Ft Bragg. If you check all lines & gas cap seal & don't find anything, it could be a failing LDP(leak detection pump), that is a common problem. The base may also have a scanner & smoke machine to run the tests on the evap system that you could use. To make matters worse, it could be an electrical problem, such as a broken wire at the purge or LDP or the ECM not commanding them on/off, but those are a lot less common.