Mast attachement - How to keep the board thin

Hello guys,

I’m building my Efoil, ordered a lot of components, have my esc box completed, motors, FR prop, waiting Nkon to restock samsung 30Q to build the battery, read, read read…

Time to build the board !

Here is my problem: I want to keep my board “thin”. I mean under 14 cm maximum would be great. I have bought a gong us rail box in foam (3.5cm thick). After reading lot of stuff, I think I have to keep my hatch at least 9 cm to fit with batteries height. 9+3.5 = 12.5 already…

Let me show you cause a picture worse more than a lot of words.

There is 2 cm in height between the red and the dark blue (hatch). 12.5 + 2 = 14.5 shit…
Yellow is where the cable will go through.
Clear blue represent the gong foam us box.

I’m using shape3D. A company in France will do the preshape for me. (you can buy a month licence for 30euros, it’s a bit hide in the website. Go to add option and select month licence). Goal is to have a design close to the lift one.

What solution can I use instead of using a high density foam box ?
What do you think about using an aluminium plate ? plywood plate ?
How could I add inserts I such plate ?
Would be glad if you could show me your solution or just give me advices.

Regards, Léo.