I bought a F1 mainframe after finding that my LL-Bean load carrier pack I had bought years ago and never used was not adjustable for torso length (I'm 5'7") and it was very uncomfortable with a heavy load. I used the F1 on a canoe trip with 3 dry bags loaded horizontally and it worked quite well but was not quite as stable as I wanted it to be so I decided to try a slightly different approach. I purchased 4 of the batwings and put one 3500 cu-in dry bag in the middle of them. I plan on getting one more batwing for a total of 5 which will make the circumfrence of the batwing/F1 match the diameter of the dry bag. I'm planning on using each batwing for a specific purpose ... stove/cooking gear in one, fishing gear in another, rain gear and outerwear in another etc and using the dry bag for the stuff that cannot get wet (sleeping bag, down clothes, etc). Anyway, I'm liking how it is all coming together. Here is my one complaint though... there should be zipper keepers on every batwing that allow the zippers to be held up when zipped together. There are loops on the F1 to mate with and one side actually has a keeper hook on it but this should be consistant across the line. I've made my own but this would make a great product perfect.
As a side note, I have 3 batwings on my pack now and they work perfectly to fit my bow in the pocket formed by them. While I can't shoot while walking into the stand it's really nice to have a pack/pouch combo that really holds my bow while hiking in. I can see how this will also adapt to the crossbow or pistol during the other seasons and with a little adjustment will handle the rifle too.
All in all Eberlestock makes great high quality gear. I look forward to using their stuff for years!