Based on my capsize tests you should probably save your money and not buy 3D bags. As you can see in this pic the bow bag is above the water level of a capsized and righted dory.

The beach rollers are tied down tight to the aft seat. Again, you can see they don’t provide any flotation when the boat is righted. They do help stabilize the boat a very small amount during righting and reentry. More pics.

Absolutely install foam under the seats as the manual says. It’s a lot of flotation as you can see here.

For auxiliary flotation I use Watershed waterproof duffles strapped in the bilges. I don’t have pics of of the duffels during capsize test. This is the same system John H. outlines in his article on auxiliary flotation you’ll be able to find on CLC’s site. It's Very effective.

I installed tie downs in front two bulkhead sections and the aft. Left ‘cockpit’ area between second and third thwarts open. Don’t want a bunch of stuff tied down where my feet are. See more tie down pics here. Click the thumbnail and read the captions for in depth discription.