You don't need to cement them down... (Less messy/easier to get apart if needed...)

This might sound crazy, but a good gasket material for bellows or between stages, etc is an open cell (light) polyurethane foam (grey or black) tape or air conditioner filter sheet... You can see through them, but will seal well after being compressed... (From your home store...) This is very minimal thickness and compresses well without much force and fills small gaps well and is light tight...

On your screws, try to get stainless steel or steel, as these will tap themselves better if the brass retainers strip... And pay attention to the head style size, so the head will fit in the hole, too... If you strip a hole, no problem just lightly silicone grease a screw and apply superglue or epoxy where stripped and thread the screw in when semi-set, and screw out when set... This will form good threads...

I have gotten the screws from the train store... A hot tip I had gotten from a model railroad guy was that the very tiny metric screws have about the same pitch as the tiny SAE screws, and the diameters are close enough to swap them...

Good Luck!!!

Steve K