I'm under TriWest (as we live in Cali, retired USAF/E7) and so far it has been surprisingly straight forward. I made an appointment, spoke with my PCM (civilian folks as we're far from VAFB) about LapBand, described my circumstance--hx of yo-yo dieting, x3 comorbidities(Apnea, Cholesterol, BP) and Triwest approved starting the process.
Hardest part was locating someone within a reasonable driving distance who is an in-network provider. Use the Provider Directory and cross reference with doc's near you (unless they are still doing it at the base).
I've three more hoops to jump through (psych eval, pre-op diet, Nutritional class) but so far so good. Good Luck!