ddw5694956 wrote an answer about Therm-a-Rest Luxury Map Sleeping Pad on October 23, 2012
I've gone camping in damp conditions with a thinner thermarest and never had a problem. Most recent 10 day trip in BWCA with multiple thunderstorms was fine, as well as some humid Wisconsin camping trips.
It sounds like either moisture/dew/condensation is coming through the bottom of your tent, you sweat a lot, or moisture can't escape your tent (you create a mini-sauna)...
Have you tried putting down some type of vapor barrier underneath your tent? I used some cheap painters plastic and cut out a "footprint" that fits the dimensions inside your tent, or a footprint that you can't see once you place the tent on top of it.
As for H20 not escaping, try opening vents on your tent to see if that solves it. If you're sweating too much, try wearing less clothes.