just FYI, you can get some stuff called fumed silica (or cabosil, Colloidal Silica, SiO2, Silicon Dioxide or Silicon Aerogel, there are a few different names). its a powder-like substance that will thicken your resin like a bodyfiller, only stronger.
you can put like 1\4" on the inside of your box, and then you are done. this is how the guys at HZemall.com do their boxes. then just fill\sand\skim\sand the outside of the box, and your ready for paint. much eaiser thatn 7 layers of glass, cheaper, and works just as well.
just thought id let ya know. its a trade secret.