On my two Juwels I use nothing. The provided frame is supposed to deal with it. For waranty reasons you are not even allowed to put something between the tank and the stand. My other tank has 1,5 cm styrofoam board between it and the stand to even out small imperfections.
I built my stand and my tank sits directly on it. If the stand is built properly there is no reason to put anything under it. I would definately not use egg crate as it would crumble under the weight..
I occasionally use egg crate (light diffuser) inside the aquarium to buffer the bottom from falling rocks, although I do not think Iâ€™ve ever had a situation where it actually protected the tank from damage (I feel it is a complete overkill protection, although overkill isnâ€™t a bad thing)â€¦
Iâ€™ve never used Styrofoam under a tank until recently. For many years I set the aquariums directly on the manufactured stand or the home made stand (Iâ€™ve made many of my own stands)â€¦
I recently bought some used tanks that are â€˜framelessâ€™ sp the entire bottom pane of glass sits on the stand. In this situation I chose to use foam on top of plywood (for a fuller support) on top of the 2x4 standâ€¦
Tanks blowing out is very uncommon, but not unheard of. But I highly suspect that almost every time a tank blows out, with proper analyzation we could identify the â€˜user errorâ€™ that cased itâ€¦
â€¦and I donâ€™t mean any offense by this as Iâ€™ve had tanks blow out and I have identified my own user errorâ€¦
I do not feel that using egg crate between the tank and stand would offer any benefits and would bring some liabilitiesâ€¦ I would have to advise against itâ€¦