I personally wouldn't recommend upgrading in Florida. we've done this and been stung by taxes etc. Last year we upgraded with Alamo from a full size to SUV because our cases wouldn't fit in the boot. It cost us 400 pounds 93 weeks rental including taxes, extra insurance etc). Once we'd got to the villa, we returned the car and reverted to the full size the following day, getting our money back apart from a days worth. It seems to almost always to be cheaper to upgrade before you go, certainly in our experience with Alamo.
8 days to go!!
Ian