The problem with open air "free air" subs is that they still need to be sealed from the front. When the rear waves hit the front waves they cancel each other out and you loose volume. Putting them under the seat really won't work. There are tons of passages that will allow the back waves to hit the front. All free air means is that you don't need a box but the front and rear still need to be sealed off from each other. They work in cars but IMO not real well in boats, unless you build a giant box.

endeavour, that is something that I have been curious about for a while.... i know that the front waves and back waves cancel each other out.... but as far as the cracks and what not letting the waves through to cancel out... i am having trouble. There is no doubt that some of the saves are escaping from under the seat but can you explain to me how this would be different from a ported box, or better yet a bandpass box (where the port is in the front typically)?? wouldnt those be allowing soundwaves from the rear to encounter sound waves from the front??

My sub is mounted in the port footwell, firing towards the helm. Not sure if its better there vs. under the rear seat, since it's all cheap equipment (came with the boat), but it's much more out of the way and doesn't take up any storage.

Ported and band pass boxes are tuned to a certain frequency. Cracks are not tuned. If you went to great effort to seal up the back storage area it would work but it would be a lot of effort. At that point it would be easier to just build a 1 cubic foot box for 2 10" subs. Obviously putting subs in the back seat panel works but a lot of sound quality and volume is being lost. My subs sounded like garbage when I first put them in. They were not sealing all the way around the rim. A few tiny air gap sealed up made a HUGE difference. It all depends on your ear and your end goals and what you've heard to compare it to..

Converted back bench base into sealed boxes for subs. Installed acrylic straps to the bottom
so that water would run under the bench base and keep the wood dry.

Nice install srl. If I didn't have the setup that I have, I would have done something Like what you did. Does your amp get hot in that location?

I installed these fans which move quite a bit of air. They are connected to a thermostat that is attatched to the amps. So far I have not had any problems with them overheating.