Yes my tank is all glass. The box is custom built in rather than mounted like a ghost overflow. It's glass with a hard plastic covering it, the bottom of the external box is a multi compound of pvc and the same black plastic as the outside of the box.
The bottom of my tank is also multi layer as well of glass, pvc and then a hard rubber on top. So if rock work were to fall over it will not harm the glass. The pvc fills in the void you would normally see under a tank and prevents the glass from flexing, so my tank bottom is completely flat and flush, no void. You could go with 100% pvc bottom also. I chose not to because that would have cost 3x as much as the 3 layer which was around $200 for my 60"x24" dimensions. PVC sheets can get very expensive.
Hope this gives you some ideas of what you can do. Better off to do it right the first time around and not cut corners if you can afford to. And do not make the mistake of going 18" wide.... 24" minimum. I would have gone 36" if I wanted my tank in a different spot... depth front to back is of upmost importance when it comes to being able to create a great aquascape.
