Modify Eastport Pram to incorporate fixed air chambers for flotation

Builder's Forum
1

Hello, 
rather then using foam blocks I would like to install some sort of a fixed air chamber with inspection holes in the Eastport Pram that I am preparing to build. 
Has anyone here done that? Or any tips? 
I guess the biggest challenge would be to to allow the finished parts to still be stackable.

Thanks for all pointers

2

I bought Holt's Opti buoyancy bags.  They fit perfectly under the center thwart.

3

Thanks.
Well in my current dinghy I currently use fenders under the seats.
But I would like to have something less improvised with the easport. 
It seems there should be room to install a floatation chamber at least in front of the mast step and under the center seat.