I think that if at all possible, you should try to get a credit card. My neice was over with us and had a little bit of trouble with her Visa debit card. She left her car rental until the day before travel!, and Dollar wouldn't accept her card. While she was flying, I was left to frantically try to sort it out (thanks again to Roger!), and pay for it using a credit card. All was fine in the end, but it may avoid some stress if you could get yourselves a credit card. If you are worried about exceeding your credit limit while in Florida (easily done, as the shopping is fantastic!), you could try putting cash into your credit card account before you travel.

Have a great time.