I agree, and I understand what you mean. Tie both bags together when you are closing them up so the bags become one with a liner in between. I agree with that.
I think the reason USMC asked was in FM's thread, it says
4) Triple bag, reversing each bag (open end to factory sealed end)
So that would not make it were you can tie both bags together when closing them up...
Guess he was asking, as I was to, which is better to do. I would say in my opinion is to tie both bags together when closing them up. as long as you have a liner in between them, you are good to go. But my opinion.. never shipped one before