Anyone cave tube while on the NCL Dream?

We are going to be on the Dream in a couple of weeks. My sisters significant other is kind of claustrophobic. We really want to do the cave tubing in Belize but one of the sites mentioned that this might be an issue. Can any of you experienced cave-tubers give me any advice? I would hate to get him into an uncomfortable situation!

Thanks!!!!

While the caves are very dark, the ceiling are at least 40 high minimum.