I am not familiar with the Tarptent but it has good reputation so some users may chime in. All tents can experience condensation, especially single wall tents. This is why I prefer tarp. On double wall tents the condensation attaches to outer wall and drips down to ground. On single wall, the condensation should drip down wall but if it's raining or windy the condensation can drip on you in tent. Not good esp. if you have down bag.

Condensation can be caused by bringing wet gear and clothes into tent, moisture in breath, sweating and evaporation of water from skin. Add two people to tent and you have double the trouble.

In conditions you described, if no wind and high humidity, condensation will be something you will have to control by wiping it off tent with a small towel if you wake up getting dripped on, or control a big reason which is sweating and evaporation. To control sweating which causes a lot of condensation, simply make sure when you sleep you do not overheat and sweat. Better to layer than take off if need be. For normal evaporation, a vapor barrier could help but will probably be uncomfortable over freezing temp.

Under my tarp in VERY wet weather, I will use the Bibler Winter Bivy at 9 oz. to keep spray off my down bag if needed. Howevery in tent if your sleeping bag is wet it is probably more from you sweating and evaporation wetting the bag from the inside out.

Chuck