take a piece of plastic window screen and build a small frame to go around it that is about an inch thick. This will hold the screen about an inch to an inch away from the glass and stop a lot of the beads from getting in there.
Leave the bottom of the frame open for beads to get out.
Also a good idea to hook up an air only gun in there to blow stuff off in the cabinet and blow the dust off the screen.
I hooked up my shop vac to the cabinet and then ran a house out the wall of the wall in the shop to blow what ever dust that runs through the vac outside via a dryer vent.
I also find that using a large cabinet with tempered glass makes it last a lot longer than a $3.00 piece of glass from home depot. I was able to get pieces for about 20 bucks each from the local glass guy. Smaller cabinets seem to get a lot of media blasting around inside. With a large cabinet, you can hold the work at arms length and direct the spray down into the hopper. I built a huge cabinet that is large enough for motor cycle frames, 5x5x3. The same piece of tempered glass lasted several years with a screen in front of it.
The air only blow gun is ideal for unclogging the suction feed line too.
-JS