Tubing is a fantastic trip and is a heap of fun to go on.  I would recommend that you consider a full body wet suit minimum.  6mm diving wet suits are best. From my experience and the cold perhaps affects me more than some people but..

• 6mm diving wet suit:   Comfortable mostly
• 3mm Full body surf suit:   Cold but still functioning
• 3mm short sleeve short legs even with polypro:   Hypothermic paralysis

Splash Gordon and other dive shops will hire full body 7mm dive wetsuits for the day if you are not sure where you can get one or are asking the question “will a bikini be enough”? 

Craig