I must apologize Mike, you are correct about the Optimas. I was under the impression that they were completely sealed and could be run safely in a non-vented situation, but after some more digging on their website, I found this not to be true. They do say that with properly regulated charging they should not emit any gasses, but in high temperatures and extreme situations it is possible and they should not be placed in a non-vented compartment.
Now I've got to rethink my plan, the Optima was going to be a perfect fit for that location. I know that most of the new Pontiacs and Cadillacs mount their batteries under the rear seat, and I believe they have a vent tube running outside the car, but I seem to recall those batteries being fairly large. Oh well, time to do some more searching....
(edit) After doing a little research, I've found that several of the BMW's use a battery with a vent tube that can be routed to the exterior of the car. I've got an Interstate dealer close to my house, I'm going to stop by and talk to them in the morning as well.
The original question still has not been answer though, what would be the best way to connect these wires?