If I were there, I sure would do it for you. I travel a fair amount and there are times a good shipping address where you can "stockpile" stuff is like gold!
A couple of ideas in case there isn't anyone here who can volunteer:
1) I have had things shipped to a local UPS store (they will accept packages delivered via postal service, FedEx, etc. as well as UPS), but there is one caveat: Each one seems to be run somewhat individually. The one near my house charges $2 per package; others seem to charge $5 (too much, to my mind!); and some have wanted me to go through a whole song and dance about signing up and registering, etc. (ridiculous). I can say that the one in Key Largo (one of the first Keys spots you get to) seems really good, and they are used to doing "odd" things like shipping dive gear and the like. There are also a fair number of German tourists who come to Key Largo, so they probably won't be thrown by "OMG, but he's coming from GERMANY!" like some might.
2) Are you heading to a "smallish" mom and pop type of motel or lodging? Or a marina? Maybe a dive shop? If so, they might be willing to hold packages for you. I don't like to do it at large places where there can be confusion, many different workers, etc.; but I've had good luck with smaller places, and marinas especially are totally used to transient boaters.
3) "General Delivery" at a small town post office. This is a service available to anyone (at least anyone here), where you just have your things addressed to "Your Name, General Delivery, Town Name, State, ZIP code" Then the post office there holds your items. In the keys, I've had things sent to the Long Key Post Office, and it is a nice "small town type of post office, right on the main Overseas Highway (about 20 miles before you get to Marathon), and very used to winter travelers, etc. You might want to check if you are going to have things sitting around for a long time to see if that's okay.
Here are a couple of contact details, just in case they might be helpful:
UPS Store, Key Largo, FL
Address: 99611 Overseas Highway
Key Largo, FL 33037
Phone
305) 453-4877
e-mail:
store4181@theupsstore.com
Long Key Post Office
68340 OVERSEAS HWY
LONG KEY, FL 33001-9998
United States
Phone: (305) 664-4112
Of course best would be a fellow SMB'ers house