This is a religious issue, Daveyou believe one thing, or you believe another. I’m a believer in Ground Cloth Under Tent, and here’s why: The main job of a ground cloth is not to keep you dry, it is to protect the coating on the tent floor so the COATING keeps you dry. By putting a sheet of plastic between the floor of the tent and nasty, sharp sticks, grinding rocks, and abrasive mud of the forest floor primeval, you accomplish that goal. Putting a ground cloth inside the tent cannot possibly do thatI mean, how could it? The very idea is absurd. It’s like taping the outside of your boots to prevent blisters.
As for keeping you drier, well, I doubt that. All modern, good-quality tent floors are coated with polyurethane, forming a completely waterproof barrier. So a floor that leaks is: A) defective, B) worn out, or C) standing in a two-inch puddle of water while a couple of 200-pound campers bounce up and down on the floor. Moreover, if moisture is getting into the tent through the floor, it will find its way into your gear, either by squirting out from under that inside-the-tent ground cloth, or by evaporating and condensing on something else.
Depart in peace, my child, and put your ground cloth UNDER the tent. Or you’re gonna go to camper hell.