how do you get the crap off the plastic ground cloth every morning ?
It stays in the air above the tent/bike, so doesn't really pick up that much crap. The only time it gets dirty is when I roll it up on the ground. If I'm careful I can keep it rather clean. It does get wet, but with any luck it's not raining in the morning and I can hang it up to dry for a few minutes. If the wind is blowing (which unfortunately always seems to be the case with me), the plastic sheet dries out really quickly.
It works so well I don't bring a fly for the tent. The tarp works as the fly; it also keeps the bike dry and gives me a dry place to sit outside the tent during the inevitable rain storm.
I was the nervous the first time I tried this system, but the plastic sheet is surprisingly durable. They cost about $1.50 and you can find them in any hardware store. On the ride home from Alaska I replaced the first one in Cranbrook, BC (2500 miles) and the second one made it all the way home to Colorado. I did borrow a piece of duct tape to patch a hole in Montana and another piece in Jackson, WY.
The photo below is the last campsite of the trip; Buena Vista, CO.