First of all congrats! I posted almost this same question a few weeks ago. I too will be 31 weeks in December and we are considering a trip. I have an appointment with my OBGYN next week to ask him about the trip.
I think floating in a resort pool at 31 weeks sounds awesome! We will see what my doc says.
After reading the replies to my post and yours it seems that everyone is different and you and your doc know your body the best. I traveled a lot while pregnant last time (sea kyaking, hiking in CO, etc.) and I felt good till I got past my due date and was still pregnant.
I know every pregnancy is different but last time I had an easy pregnancy with no complications. And like you, I stayed in great shape. I'm sure the doc will make his decision on that same medical history.
All that to say, we are going (again, as long as the MD says it's ok)! Eveyone in the group knows that we will be moving slower. And since we will have my 4 year old with us, I'll get to go back to the resort and nap.

And let's face it, at home when she naps I clean house!
One tip someone gave on my thread was to check insurance coverage for out of area hospitals just in case. I thought that was a good idea.
So, maybe I'll see you there and we can share a bench and eat dole whips while our familes ride Space Mountain!