Can't help with Florida, but we transit the US crossing at Detroit November 1st, going through Indiana, Tennessee Arkansas Texas and New Mexico and Arizona to get to southern California December 1. We do the reverse trip starting March 1st to arrive back home April 1st.
Going down we have no problems without reservations, we use the "open all year" parks in the north and we de-winterize in Bowling Green KY. On the way back we have found we need reservations in March due to the Spring Break weeks which seem to vary in each state. The KOA website is a good one to check for vacancies , they are good for short stop overs. We also travel short distances, getting into parks in the early afternoon.