AWOL:
An 8x8x8 boolean array would still occupy 512 bytes of memory, SRAM or flash.
If you store the values as bits, that reduces to 64 bytes, but you'll have to do some of the addressing legwork yourself, with bitRead operations (or shifts and bitwise-AND operations if you're comfortable with those)
I tried that site already, but most of the explanations are for String-arrays so I'm getting too confused when reading that.. :~