Large format film holder ..how to attach it and make it light tight to wood /cardboard?

Im wondering if theres an easy way to attach a film holder to the back of a cigar box/ cardboard box simply using an elastic band, weather stripping and strips of cardboard? Any photos? How obsessed should I get to make it light tight?

Im in that (everything is a pinhole camera phase) but wanting to build one that can use a film holder.

Any DIY or Pics?

I made a 4x5 pinhole camera out of foam core and duct tape some years ago. The key is to make a groove or channel in the back of the camera to fit the raised feature along the end of the film holder. The back also has three "walls" around the film holder - to block light. In actual use, the film holder is held in place by two suitably sized rubber bands - which are not shown in the photos below but if you look closely, you can see where the rubber bands have left slight indentations in the foam core.

I've used half inch wide rubber bands. As long as the holder sits snug, it'll be fine.