It depends on what time of year you are there for the bugs. We went end of February and had none. They have a rainy season, that is when bugs are bad. We took bug spray, and had no problem. They have restrooms right were the buses park before you make the 45 min walk to start of river. When you get done with the tubing, you are a very short walk back to parking and restrooms.
Oh and be careful what you bring back, next morning husband was shaking his swim suit and a huge bug fell out. It was funky looking. Dont know when he picked up bug, we changed in restrooms after the tubing. Glad it was him and not me