I was going to say something about the heat, but if you're going in Dec, that might not be AS big of an issue as if you were going sooner. Then again, from what I remember of xmas breaks in Miami during college (the fam moved to Miami the day after I went to college), it doesn't really get COLD all that often... (editing to add....then again, I recognize that Miami is a bit further south than Orlando...)
The Moby does stretch and you do have to re-tie...I never really had to re-wrap, just sort of did strategic quick un-ties and pulls and got it tighter that way. But I also did lots of Moby-style wearing with non-stretchy fabrics, and they do almost the same thing (the Didymos might not do that)...
All that said! I'd get a comfy mei tai or an Ergo, and get your back-carry figured out for the trip.

I never had a sturdy mei tai (mine was in a summer mesh for the body) and it got painful as DS got heavier, but I hear a good one with padded straps and sturdy body panel is just faboo.
The Ergo is probably my favorite, though, in terms of being able to carry the wee bairn for LONG distances with little effort.
But if you want to do the Moby, I see nothing horribly wrong with that, it just might be a pain to re-tie or re-wrap, since baby will be a *bit* bigger then than now.
