I will need to use some plastic rubber or something similar on the inside to seal the corners, because with the leather off the camera, the corners will usually not be light tight.
This may not be necessary. I plan on stripping the remaining leather and then filling in the finger joints with some high quality wood filler. The joints are already so fine it won't take much. That should be all it takes for making it light tight. A final sanding with very fine sandpaper (up to 600 grit), and then a coat of varnish should make it shine.
"There are two ways to avoid most trouble in life: live below your means... and within your seams."