What foam board are we using ?
We have replaced foam core and Gatorboard with Infinity board. This solves a large problem – warping due to changes in humidity. Gator is much better than foam core, but not perfect. Both have a styrene foam core. Foam core has a paper based outside liner. Gator has a wood pulp based liner. Both absorb moisture and can warp when the humidity rises. Warping happens when the front, back, and foam center absorb moisture at different rates.
Infinity does not warp because it has a styrene foam center and a styrene exterior. Neither absorb moisture.