Front Hatch Insert

I’d like to make something out of a foam material that will fit inside and fill up the entire front hatch of my outback. The idea is that it would add buoyancy and keep the gear I normally store in the kayak hull organized and in place; I would cut out small compartments to hold items like the FF battery case, bilge pump, and so on.  I want this to be removable so I can take it out and use the hatch for storing gear if a situation requires it.  I’d like the foam material to be similar to what the pool noodles are made from so it can be cut and modified and will not break apart like Styrofoam.  I’ve been trying to find this in 1 or 2 cubic foot blocks, but so far no real luck.

The other idea I had was to use that expandable foam insulation, but I quickly decided that was a bad idea because it is not meant for being submerged it will likely become water logged.  The other thing I’ve come across is that two part foam solution guys used for boats; I’ve never used this before and don’t have a good idea what the material is like after is sets, but from what I’ve seen it looks more like Styrofoam and seems like it would it a PITA.  Has anyone ever used this before?  Do you think it would work for my application?

Any suggestion, recommendations or ideas for this are welcome.

I would not use any two part or spray foams that expand. You risk deforming the hull of your kayak as the foam expands and pushes outward on the sides. I have experienced this with cooler lids filled with spray foam in order to provide more insulation.

You can probably get some free dense cell also called "closed cell" foam from an appliance store typically used in large appliance packaging.

I just use a large dry bag that I stuff in the front hatch. It works as flotation and keeps other things like the things you mention. Ive also got a Tubtrug up there but is a size smaller that makes a handy tote. similar to this but not as permanent.
http://www.northwestkayakanglers.com/index.php?topic=13375.msg146932#msg146932

Have you considered an inflatable air bag such as those used in sit-in kayaks?

Thanks for the input, you guys have given me things to think about.

Another option is a closed cell foam archery target.

You can get 3 inch thick sheets of foam.  All it would take is gluing a few sheets together to be as wide and as tall as desired.  Then you could carve it to the desired shape.

For buoyancy I stuffed pool noodles inside my hull as they are, got a dozen to fit in the tuna.

You can find 3-inch thick sheets of closed cell on Amazon in various length/widths.  Not terribly cheap as I remember, but they're offered in different densities, and I was looking at semi-rigid - the most expensive - so I could sculpt it.

Buoyancy will only be in effect if you take on water.   It will also displace the incoming water. But with that, do you want to have it push all the water towards the back making your kayak butt heavy and even more unstable if you are taking on water?