Gorilla pad over xps foam

[Astross89]

I read some people still added gorilla pad over xps foam.

A. Should this be done?
B. What stops it from shifting over the slippery foam?

 

[bkstyles]

I did this method this past week. It’s only been one weekend since installing and one pool usage day. The gorilla pad and XPS held up well. The weight and pressure of a pool full of water should keep everything from shifting underneath. Good luck.