Water condensation issue inside TJ

Do you notice it only at certain times like rain? Being winter snowy boots? A smell of coolant? While I am blessed with a ride that does not leak I do know that moist air must come into contact with a cold surface to condense.
 
Check out the windshield gasket if it leaks.
 
With a helper on the other side, take a bottle of compressed air (the can you buy at Office Depot works fine) and spray around windshield gasket. If you don't have a helper, spray something that foams a little around the outer side of the gasket and then spray the air.
 
There is no definite answer about the specific reason it is happening. You'll just have to check any and every source of moisture.

Several things to look for have already been mentioned, I'll add large dogs in enclosed vehicles as something that might be causing it.

Good Luck.
 
I too am wondering about the heater inside. Do you mean some kind of space heater, placed in the Jeep itself? Sounds risky, but I'm curious.