How do your gaskets look on the refrigerator door? Are they broken? Is it making a tight seal? THere is a drip tray, on this model it can not be removed and sits under the compressor. The water that goes into evaporates with the heat of the compressor.
If you pull the unit out, there is a drain tube for the defrost that runs down the back of the unit. Check the tube for any blockages as well as the hole that goes through the liner where the tube attach's.
The moisture switch should be left on, it reduces moisture around the from of the refrigerator.
Is the part that the tube connects to clear? There should be something that looks like a little sink drain trap that the tube connects to.
If the drip pan is bone dry, you must have a blockage of the defrost drain.