sorry nyxi have not done the combo excursion but Cortney my wife and I did do the cave tubing last month.
We did it through cavetubing.com. This is something that i had always wanted to do. I would reccommend going to a reputable outside company as you get a alot more for a lot less money and it is their job to get you back on time.
As for the excursion itself the company did a great job, we took about an hour long bus ride to the river. Along the way we were given a guided tour and the guides were very entertaining. Once we got to the river we were given a chance to change ( there were real bathrooms and change stalls... very civilized). From there we grabbed our tubes and hiked to the drop off point. The walk through the rain forest was great. Very hot and again we were given lots of info about the flora and fauna.
We dropped into the river and they hooked you in chains of eight tubes with a guide in front. You actually spend most of your time in the caves (we went through 2) You spent 20 -30 minutes in each cave. I am not claustrophobic but can't imagine that it would bother you, the caves are very large and you don't get to close to anything to give you that claustrophobic feeling.
After the second cave you spend another 15 minutes floating back to the starting point. I actually wished that we had spent more time on the river outside of the caves.
We had a great time, wouldn't do it again because I already have and it wasn't really a thrilling tour. We loved the walk in the rain forest and found the tubing a little long. Knowing what I know now I would still have done this excursion and think it was worth the money. We paid $45 each for the day and we were back to the ship with a few hours to spare.