Nikki:
As someone who is also mildly claustrophobic, but thought this would be "no big deal" (and recalls going on the 20,000 Leagues ride at WDW when I was younger), I have to be honest and say that I WOULD NEVER DO THIS AGAIN.
Admittedly, our sub was overloaded since they boarded everyone from the ABD trip who wanted to go on a single sub (40 of us?) and the experience was made even less pleasant by the fact that we seemed to hop off of the track at the beginning of the ride and then bottom out several times throughout.
It also wasn't reassuring to hear the pilot talking to home base asking "What should I do?" and to hear them answer "Just keep going!"
Then there was also John (3guysandagal) shouting, "I feel water by my feet!"
There
was air movement in the vehicle and I just kept staring out the porthole and taking deep breaths, so I "survived," but it wasn't fun for me.
Besides, if you've been on the Nemo clam shells in the Living Seas, you've seen the basic technology and "show" anyway.