Several people have mentioned trying to keep the transmitter and sensor site dry when showering and feeling that it does improve performance.
I've had several times that I felt that a long shower caused the sensor to start performing poorly without much recovery. One reason I like arm sites better than my stomach is that it's easier to keep them somewhat dry. After a long shower on Monday, the sensor never recovered and I pulled it out last night. It really was only a good sensor for a few days and then mediocre.
So right now I've used two sensors. One failed completely and the second one was mediocre. However, both of them had days when they were fabulous, so I'm still optimistic.
But back to the question. How do you keep you site dry? How do you cover it? I've occasionally put plastic wrap on top of it with tape on the top only. (The time I taped all around it, some water leaked in and I had a swimming pool in there.