pepper'scove

I have a few questions about compression foam used underneath larger tanks.

1. How thick is the foam you usually put under your tanks?
2. What type of foam do you usually use?
3. The neoprene foam on this website seems like a good choice. What do you guys think?

My tank is a 21" tall tank (It's a standard sized 75 gallon). Assuming that the pressure ratings found at the link above is rated in psig (gage pressure) and not psia (absolute pressure), then the additional pressure due to a 21" ...