Wish I was in on that trip! But, we did go down that way in June. The Sea Dell Motel is a great place to stay in Marathon. Parking is kind of cramped if you have a trailer,

but they are good to work with you. The place is very clean and reasonable considering. If they aren't real busy, they will work with you on the rates a bit if you try.
If you are riding around up 'north' in FL, the Clay County Jail Museum is great.

I will try to get some pix up some day. The jail won't take too much time, but it was a lot of fun & a good break. My only time ever behind bars.
Oh yeah, a couple of great places to eat is the Keys Fishery in Marathon, It is on the Gulf side, I think at 36th street. The other great place is the Square Grouper, it's at the 22.5 mile marker (I think), I don't have that shirt on. :s I am wearing the souvenir from the No Name Pub, on of course, No Name Key, off Big Pine Key. Watch out for the Key deer, tiny little buggers.
Have a great trip, we've spent quite a bit of time in the Keys, PM me if you have any other questions. I'll help if I can.