I'm going on the 12th as well but friends are picking me up, so that will be one less car.
Are you coming from out of town? If so, have you checked the possibility of parking near Hobby airport and taking a shuttle to the cruise terminal. Some of the off airport lots charge around $6/day. I don't know what the shuttle fee is but if it is around $30, you would break even.
Also, your car would be safe from flooding if another hurricane comes in while we are cruising.
By, the way, if you were a rocket scientist you would alreay live near Bayports because it is just a few miles from NASA. ;-).
- Tomcat