The area under the round hatch in front of the seat in the Outback and the Revolution is a great place to store items which you want to be able to get at easily when you're on the water, and there is a lot of room under this hatch. However, the area is pretty shallow, and in order to use that space you have to overcome the following challenges: (a) Pieces of gear and dry bags need to be small enough in diameter to fit through the hatch, and short enough or flexible enough to turn a corner as soon as they go through the hatch. (b) If you put a small loose piece of gear such as a water bottle in the area under the hatch, it's likely to quickly migrate to a location where you can't reach it. (c) When you open the hatch, water runs off the top of the hatch and into the area under the hatch, so whatever you put inside the hatch is going to get dripped on and be sitting in a little puddle of water. (d) In order to fit into the area under the hatch, a top-loading roll-top dry bag needs to be small in diameter, flexible, and not packed too tight, because the dry bag needs to be able to bend as soon as you cram it through the hatch.
One option is to buy several small, lightweight, flexible, roll top dry bags in an assortment of colors. Pack them loosely, and slide them in various directions from the hatch. The different colors will help you locate items. For example, you could always put your lunch in a green bag. You'll probably need to haul a bag out through the hatch in order to get at its contents, particularly if what you want, say suntan lotion, is at the bottom of the bag.
But here's my solution: two 10" diameter duffle-style dry bags, each about 20 inches long. I roll them up and slide them through the hatch with only a few items in them, and slide one duffle bag to the left of the hatch, and the other duffle bag to the right of the hatch, with the long opening of each bag under the hatch. Then I finish loading the bags when they're in the area under the hatch. I can put big items like a sweater in these bags, and the bags keep small items from migrating. And the mouths of the bags run the full length of the bags, so it's easy to paw through stuff which is in the bags while the bags are in the area under the hatch.
One of the dry bags I use is an old 10" diameter Watershed dry bag. It was one of the first bags manufactured by Watershed. It has a ziplock style of closure which is easy to close from outside the hatch. Unfortunately, Watershed no longer manufactures duffle style dry bags that small. The other dry bag I use is a Mad Water 10" diameter duffle-style dry bag with a roll top closure. See, for example, http://www.thewaterproofstore.com/spdf30l.html
. These two dry bags provide me with a large amount of storage space, and because they are dry bags, they protect their contents from water which drips in the hatch, or pools up on the floor. I usually don't bother sealing the mouth of the roll top bag, which is a hassle when the bag is inside the hatch. I just orient the mouth so water won't drip into it