Slim BlueROV2 for caves

Hi All,

I would like to modify the standard BlueRov2 to be a bit less bulkyt to get into more places that I can’t fit. I’m planning to replace battery compartment with two slimmer ones, e.g. two slim tubes with 4-4 26650 batteries. I’m also aware that this 2x4 setup is much worse than “brick” LiPo batteries with respect to possible current draw.
Is there a good DIY soution (or cheap commercial one) to create “brick like” battery compartments that endure e.g. 70m dives? Cylindrical housing is a big waste of space…

thx
Dénes