Snap! I'm in Florida for a road trip for three weeks in September too.
Reserved exact model via the Hertz Adrenaline Collection (but reservation made months ago), got a convertible Camaro which JUST takes three men and luggage (if you don't mind a bag on one of the back seats while the top is down). I don't need an ITDP but I got one anyway, a friend of mine got pulled in Nevada for misdemeanour speeding and Highway Patrol were happy with UK licence only, but as I said, I got one anyway.
Most looking forward to driving the Oversea Highway, the 'glades and also a trip around the pan handle to New Orleans. Gonna watch the Miami Dolphins (well mainly their cheerleaders ) too. Have fun, keep an eye out for us in the Camaro.
Don't forget your ESTA too
Edit- just found this
R – USA (Florida) compulsory IDP – 1 January 2013
A law was introduced in Florida, USA, on 1 January 2013 requiring all persons who hold a licence issued outside of the US to carry an International Driving Permit along with their national driving licence.
The Governor of Florida repealed this law on 2 April 2013, however, car hire companies and insurance companies can impose their own terms and conditions so you should check with your intended hire/insurance company prior to travel or obtain an IDP as a precautionary measure.