Thanks everyone. We have decided to try Cobalt Coast. One reason is we can fly direct from BWI to GCM and won't have to worry about transferring to LCM and missing our flight back to BWI like we previously did. Are there any rental car companies that will deliver a rental to the resort?
If you want a car for the week you can make a reservation and pick it up at the airport, sometimes you get a better rate if you reserve for a full week.
Transfers to/from the resort are provided so if you only want a car for a few days, I think that the resort can make the arrangements and have the car dropped off (or they will pick you up.) At least that is how it has worked for us at LCBR and CBBR, but I don't know if it works the same on GC. We always get the rental car at the airport on GC.
But I think you should reach out to Clearly Cayman and/or the car rental agencies and ask about it soon. You will be traveling during the peak season so you should get a car reserved in advance and not wait until you are on the island. It's a busy time.