Question on foam for under a rimless tank

[chazde3]

I recently took a 30g tall tank and flipped it on is side on resealed it so that it is a shallow 30g cube. This means there would be nothing between the glass and the top of the stand I am building. I plan on adding foam under the tank to prevent any issues with the glass touching the stand. My question though is what kind of foam should I put under it, a denser foam that wont compact as much or a less dense foam that would compact more?