take the 35mm sleeves--plastic kind and get a device for food sealing known as the "euro sealer"---for heat sealing of opened chip bags. these can be used to weld the plastic on the 35mm sleeves in half--I use this method for 16mm film strips from the minolta 16. You can make smaller or larger slots as you please. Making straight lines is a challenge--you have to set up some kind of sliding ruler to do it. DIY--"on the cheep" "smart cookie" you'll get chicks.
hey--I just thought--USE STAPLES to put in dividing barriers. Easier and everyone has a stapler. Quick and dirty.
– that sounds easier than the soldering iron technique in that video.