It's been done before and is not the best solution for floatation. I've read a number of threads where this is discussed quite extensively. The arguments against seem to be mostly that 1; the bottles will shift around. 2; the bottles will collapse under pressure, 3; bottles will expand and contract with temps.
After all this I am still considering doing this in a modified form and will explain.
I have 2 large floatation boxes in the stern of my Sea Nymph. They are each about 5 cu.ft. buy my best questimataion. The pour in foam kits being sold are either too little, too much or have to mix different size kits which gets costly. So my thinking is to use heavy walled plastic containers as a filler and encapsulate them inside the foam. This will prohibit them from shifting around.
The other 2 issues, expansion/contraction I'm not going to worry about because the I don't believe the temperature swings will be great enough to be an issue. Collapsing, let's think about this. The whole idea and purpose of foam is for floatation, hence the term, which originally was "level floatation". The theory and practice was meant to keep the boat from 1; sinking and 2; to keep it level and prevent it from capsizing.
The idea is to displace water with something that adds to floatation. So how much pressure is required to compress and collapse a plastic container and then how much pressure is required to collapse that container when it is encapsulated in foam? More than the pressure of a swamped hull? If the gunwales are under water the boat has technically sunk and it doesn't matter how much foam you have the occupants are not going to be able to stay with it..
