Do they require prepayment or deposit?
If yes, is it refundable with a couple hour notice (like hotels)?

you can call toll free number at (877) 890-7444 Extension 1

no prepayment or deposit is required

Actually...there is a prepayment up to 3 nights rental fee on the marina and there is a 30 day cancellation ....if you are within the 30 days they will work with you to move it but will not cancel and refund inside 30days. I called because I rented there and I know I had to pay a deposit. So...the information above is directly from me calling the toll free number.

required is the key word, we have stayed several times and just called on 16 and reserved a slip. Unless there is an event, Scrub is generally dead.

It all depends on whether you reserve through the Florida office or contact the Scrub Island Dock Master directly to check availability. The Florida office will most certainly ask for credit card confirmation whereas the Dock Master will take the name of the boat and hold a slip for you.....I would call the resort directly and ask to speak to the Dock Master. It all depends on the time of year and the particular week you are sailing - sometimes the marina is completely full and sometimes it is nearly empty.........Don't forget to ask for your TTOL discount, which seems to be a seasonal discount.......:)