I made something similar some time ago from foam-board and hot-glue.

I found the corks from sherry bottles (they have a 'bulb' on them) make good handles - just hot glue the cork end to anything that needs a knob.

Durst made a version that had a sliding cover over the exposure slot: the cover had a pin you pressed into the paper and this advanced the paper under the slot each time the cover was moved.