We put the gravel down on top of the dirt floors. There really is no need to remove the gravel when the mats are put down, just put the mats on top of the gravel. If we had went with the French Drain it would have been far better to do, though. A French Drain, as I recall, is a trench dug in the stall to about 3-4 feet deep then fill it with gravel to the level of the stall floor. Then bed the stall as usual. The moisture and urine will flow into the gravel-filled trench. Putting powdered lmne down on the floor of a stripped stall is a very good idea. It sweetens the smell of the urine.