I attempted something like this a month or two ago. Dimensions were roughly 64x64x64 cube. USed onplayerinzone, I think, Ill have to dig up the save, though... The main problem I had was that the output tables (two, one for the vertical and horizontal planes) would read you just outside the zone and place your in cube spaces you did not occupy. Thanks to you, I may actually go back and work out the bugs, the vast majority of which prevented me from completing the project.
Edit:
If you need proof, then Ill be glad to post a current copy while I finish the touch up.
Touch up is merely cosmetic to ensure that all zones are created and to cut down on the number of events.