This is a "Beartrap" or "Landmine" topic, it always ends this way because there no data on the subject.
Having fallen into this same "Beartrap" myself, I spent MANY hours researching it.......
1. Other than this application I was not able to find another application that uses "foam" under direct constant loading.
2. As discussed, the glass tanks are primarily perimeter supported, and the acrylic need even load distribution throughout.
3. The "foam" people speak of and use varries GREATLY. Some use open cell, others closed cell. The Engineering properties varies with each product and performs under loading differently.
4. There is very little data on their behavior under constant loading of these materials. Especially with failure due to fatique.
5. Foams and rigid insulations commonly mentioned and used were originaly designed for insulation purposes only, they were designed with minimal impact forces in mind, not constant loading.
6. As the tank gets bigger, the stakes get larger. As psi increases, what may work for smaller tanks, may not for larger. See the chart below I quickly threw together at the time to illustrate this.
7. Semi-Rigid bodies such as these materials, do not follow the same Engineering theory than that of the rigid bodies we are familliar with. The way the bonds are arranged, the cell structures that are used to carry this load is difficult to obtain.
I found this quote in a preview of a journal article I that uses words other than my own.
"On the Crushing Stress of Open Cell Foams
The compressive response of many foams is characterized by an initial linearly elastic regime which is terminated by instability. For open cell foams instability leads to localized buckling and collapse of zones of cells. Local collapse in these zones is terminated by contact between cell ligaments. "
The main problem with this discussion is: Nobody can really tell until it is tested. You see, foam is a semi-rigid body and varies with different compositions. Its at the point that it is settled and compressed that concerns me. Discussions of dynamic loading, sheer strength betweem the two planes, a failure due to fatique have never been considered, especially factors of safety.
In my research before, during and since the last discussion on the subject, I dug through each of my Mechanical Engineering textbooks looking for a similar application, researched hours of articles on the subject, even consulted with several of my peers who are also Mechanical Engineers on the subject, even going as far as to ask the wife of a friend who is a Materials Engineer with Lockheed Martin. All had the same response I have, "Maybe, but I wouldn't risk it."
This is what I have discovered in my research on the subject and thought I would share it with you guys, please use it to ponder to make your own decision.
Personally, I would focus your energy on quality craftsmanship, and top it with a contigous flat surface, eliminating the need for such materials. I plan to use Corian on top of my stand next time.
