I don't use eggcrate at all. On medium sized tanks (e.g., 75 gallon and smaller) I usually use plexiglass placed right on the tank bottom before adding rocks or substrate. On my 180 (and several 75s) I use thin sheets of slate that sit right on top of the glass. The 180 got slate stepping stones from a garden center - just the right size, good protection for the glass bottom, and if the digging cichlids expose it, it looks very natural.
Jim