We will be staying in Sian Ka'an at the end of February for 6 days. We are trying to decide whether to rent a car from the airport or to just get a transfer and not bother with driving. Can anyone give us insight as to the ease of driving from the airport into Sian Ka'an? I have read the road in the biosphere can be challenging. We've traveled to and driven on islands like Vieques, where the roads absolutely require an SUV. So we aren't fearful of that sort of trip, but would like to be prepared--do we need an SUV or will a regular car suffice? Also, any reccomendations on specific car rental agencies would be appreciated! Thanks!