Keep it simple and use gallon size heavy duty FREEZER BAGS.
These will also take 5"x7" holders but the 'extra' space and build quality are both a buffer against misadventure as well as the abuse of carrying, reuse, and too tight a fit.
Do not over fill the bag so it is being stretched across or at the corners of the holders.
Just remove the air by only 'zipping' the fastener about 90% up, fold the excess bag snuggly, removing most of the remaining air and finish closing it up.
Personally, I do not tape the folded bags and I recommend you don't either, using paper slips inside to note which films the bag is carrying.
Cheers