Yea, i use it sometimes at work. I dont think it will stick to the plastic but you can totally make any kind of box or shape with it. You just need a mold.
Styrofoam works great. make your mold from foam. then get all your sheets of glass ready, all your tools(metal roller,paitbrushes,electric sander or sandpaper, LOTS of rags, scissors,a really dull paint scaper,sheets of plastic),gloves,wear old clothes,get everyhting you might need.
Mixing the resin can be tricky unless you use the 50/50 mix stuff, i have never used that stuff so IDK. I used the 98/2 mix stuff in which case be REALLY carefull mixing. One or 2 drops to much hardener and it will start making A LOT of heat. Like,burn your hands hot. And it will get hard too fast and wont be strong.
Once you have all your stuff ready wrap your mold in plastic (or some kind of heavy wax if you have it) you just lay your sheets of fiber on the mold and paint on the resin, making sure ALL of the fibers get wet. and no air bubbles. Dry fibers or bubbles will create weakspots, once that weakspot flexes it will spread. Then put the next layer on, paint with resin and use your roller now to squeeze out some of the excess resin. Keep doing this untill you have all your layers on. Dont be afraid to make thick spots where you will be mounting.
Stager your layers! You dont want the edge of the sheets to all be in one spot. Like if you lay one sheet on and it covers one whole side of the box, then your next layers edges should be 1-3 inches to the side of the first. Orelse the glass wil crack right at the edges.
Pay special attention to corners and edges make sure that all layers are touching eachother.
Beware, even if you do it all right the fibers will try to lift off of the surface!!! keep checking it every 5 minuets untill it is dry
Idealy when you are doing flat surfaces and you get all your layers on you would lay another sheet of plastic on top and squeeze out as much resin as you can. But you are just making boxes so it should not matter.
Anyway, thats just the rundown.The first 2 times i used it i left to much resin on and the whole thing was heavy but not so strong. the glass is just there to hold the fibers. Anyway be prepared to make 2-3 boxes before you get one that lasts forever
you might want to read some guides on the net. But once you get the hang of it then its easy shmeasy and you can make just about anything real cheap
edit- If you build the structure out of wood first, then coat with glass it will be HELLA STRONG (think speaker boxes that dont rattle)