EASY BAG USE - NO NEED FOR TAPING ETC.
IMHO you don't need to do all that in the video for your bag. Try this exercise and I think you will see that. The only purpose of the "band" is to hold the bag on top of your head while it inflates, and then, once you slide the bag down, the band will hold the bag in place at your neck.
You can buy an elastic "wrist sweatband" or elastic sweat headband if you have a really large neck. These are very cheap at Walmart, and are the kind you see tennis players wearing on the wrists, head.
To see how it will work, first stretch the wrist band around the top your head at the spot where the bag will be inflated. Then slide it down to your neck and let loose of it. It should feel snug but not uncomfortable. If it does, you have your band.
Now, scoop up air from your room into the bag, or gently blow into it to open it up, like you blow up a balloon. This is to stretch out the bag from its folded condition.
Afterward, scrunch the length of the bag, from top to bottom to make it tall and skinny, so you can put your band at the top and pull the bag up through the band, until the band is now about 2-3 inches from the bottom of the bag. You can just fold the 2-3 inches of the bag's bottom up over the band.
Then when use the bag, you simply grip the band and bag bottom together with both hands, pull it down on your head to the position it will be when it is inflated, It will easily stay in place. (You will try this in rehearsal, with no gas on of course).
Once you establish the place on your head where the bag will sit to inflate, you can now practice pulling the bag down slowly and gently to your neck. Do the same thing as before, with both hands on either side, grasp the band and the bottom of the bag (that is folded up a bit), and lower the band to your neck, and let loose.
You will find the band used this way will firmly hold the bag atop your head, and also around your neck snugly, but not at all uncomfortable.
Now that you know the elastic band will hold the bag in place on head and neck, you can rehearse.
The bag is now ready to test inflation on top of your head. Just grasp the band and bag together, and it moves up and down easily. No tape, no seam, just an elastic band.
After testing, I kept everything together and placed it in my closet, ready.