Yesterday I gave machining an 8mm strip feeder with a dovetail cutter a try. Material is 10 mm thick polyethylene, which isn't very rigid and makes a lot of fuzzies (even after trying to sand them away), but is quite cheaper than acetal, so it's acceptable for the prototyping stage.

The dovetail angle is 45 degrees. The tape fit was quite tight, so I think I'm gonna change the angle to 60º and play with the dimensions a little bit more before I publish the tray design file.