I have BCBS and my BMI fell below the requirements once during my 2 year history and I was still approved. The guidelines say they evaluate this situation on a case by case basis.
Definitely not a automatic rejection!
I wish I could offer some advice but instead I plan to take any advice you get on here and lock it in the vault! My surgery isn't until July 29th but I also travel a lot for work and have the same questions and concerns as you.
But....how great is it going to be to fit comfortably in an airplane seat????