I've never heard of a Lipo bag but is it safe to assume I don't have to use one and that I can just leave the batteries in their slots of my Nanuk 915 case?
I don't mean to drive this into the ground but I want to make sure I don't have any issues since one of the main reasons I'm going to my destination is to get footage with the drone.
Yes. if the batteries are secure and the terminals not subject to hitting anything else, you are fine. Your setup seems to meet that criteria very well.