Let them hang on the side of the fence, wall, or some times they have clamps inside the car wash stall to hang mats. This should do the trick. You can let the degreaser / 409 / mean green sit on the mats longer if you like. read more
Wash one chair pad at a time, use the gentle cycle, and make sure your machine has enough space — if you're forcing the pads to fit inside (they may not fit if your machine has an agitator), to wash them by hand instead. read more