Best/Simplest/Easiest way to secure a lid This is a part I designed, a kind of a frame:

Into the frame I want to be able to place a flat object of variable (but uniform) thickness - like paper, glass, sheet metal, etc. The inserted object should then be covered by some kind of a lid and secured. The lid should keep the inserted object pressed against the "ledge" you see in the frame. The object in the frame will be repeatedly replaced, so the lid will be repeatedly taken off and placed again. When placed, the lid needs to hold, not fall off randomly.

What would be the best/easiest/simplest way to secure the lid? Considering ease of printing, so ideally no supports, as little additional separate parts as possible (but adding a few is not a big problem), etc. The side of the frame you see in the picture can be modified, stuff can be added.

Considered: 


threaded inserts in the corners of the frame, screws through the lid. Screws are a little impractical. Threaded inserts for screws big enough to be practical when handled repeatedly take up a lot of space both in area and depth
rubber bands stretched from one side across the lid to the other side. Rubber bands seem a little weak to hold the lid securely, but I guess it could be done.


What methods would you choose?
Don't know how big your parts are, but if repeated use is a concern and you need pressure that screws can deliver, consider screwing on some toggle clamps if you have the real estate.

You could also make a 3d printed version of one that's sized to your needs.  There are some models available.