Xps is degassing. There is a reason why white foam is used 99% of time, its stable. Plus cost.
You would be way better off to put a layer of thin wood on top or bottom or both. Even a veneer would do.
Thats to prevent dents which will ultimately delam the core from glass.
Than u could use less glass/cf and save money/weight etc.
3layers glass to go at once is not for beginners. It takes time to master this.
Double check the weight of all, plus resin. Than add 20-30% on top if not using a vac. Carbon with no vac is degassing trouble.
I see u 100kegs? Man, u need a 12cm thick I-beam board.
And that I-beam u can imagine as rail tracks, wide on top, narrower on bottom. Thats how the race boards are built.
Simply put, one hit to sea bottom with a wing nose will rip the inserts out because of your weight and the leverage you are placing on the board. Not ideal. Thicker the board more chances not to rip it.
Back to you