Okay, I made significant progress this week with the plate holder itself, including the light trap....
For the light trap, I used 1/8" stainless steel tubing and routed out a channel in the thicker side of the plate holder with a 1/8" inch bit. Then I routed out a small U channel on the underside of the trap cover with a small coving bit and glued in some black suede. The two springs at each end were thin piano wire bent sharply so that 1 1/2" goes into the tube and the little legs stick down. Now comes the fiddly bit of holding it all down while the cover is screwed on. The good thing about having screws on this side is to allow for service and cleaning of any gunk that is likely to get in there. Next will be making locking tabs to secure the platholder into the rear camera frame, and rear door and locking tabs for that aswell. Then everything inside will get a seal coat of matt poly, and then painted flat black. The outside will get a poly finish.
The darkslide is 1/32" XX Garolite phenolic from McMaster-Carr. Looks like regular darkslide material. Now I've got to cut the slide down and add a handle... Easy peasey lemon squeezy.... as they say.
Next I have to build up the back of the plate holder with a door that secures that plate from the back. It's all down hill from here!!