Need help planning a Peli case sub (foam selection, volume, sealed vs PR)

Utter newb here.
I've started work on a project I've had for a while - namely converting a pair of Genelec speakers into bluetooth (heresy!!!!), battery powered ones that auto-pair with eachother (think airpods).

To carry the speakers, i've gone for a Nanuk 935 case (peli 1350 equivalent), and once the speakers are out of the case, i'll have a lot of usable volume within it which would come in handy to expand this into a 2.1 system (the BT boards i'd be using allow for this)
The case itself, when empty, has ~28L volume. Of that, a small portion will be reserved for the batteries, transformers, and componentry necessary for the sub to function. The rest will be filled with some sort of open-cell foam to keep the speakers secure during transport.

I will reinforce and dampen the sides of the case as much as I can, but given the material of the case there will still be a substantial amount of flex, at least when compared to something like MDF.

How would you approach this? Initially I was thinking of just winging it by calculating volume w/foam and buying a couple of those TB sub + passive rad kits, but i'm unsure whether that would be a good idea. I briefly considered a port, but i'd be running into issues with internal layout interfering with port length, plus it'd be nice to retain a modicum of water and dust protection.

Any idea on which foam and driver/s would be best suited for this? Keep in mind i'm limited by the size of the case, so even 8" would be pushing it.

Thank you very very much!
Use the foam that comes with the case.
Hey! Thanks for the reply.

I am in contact with Nanuk and they are offering several types of open-cell foam. As the foam will be laser-cut, i have that additional choice, hence the question!
The pelican case may not have the rigidity to make a decent sub without some substantial reinforcement.
I realize this, the sub case is mostly just an additional extra to reinforce the low-end of the speakers, and as this will be carried around and set up in untreated spaces i'm not really expecting it to be extremely accurate. Nonetheless, i do plan on using some sort of metal or composite reinforcement on the larger, unbraced surfaces.