I needed to work on my AC after getting my car painted and wanted to keep the fresh paint as nice as possible. After a bit of searching I found this on another forum.
Clean the body area where you will be working. Put a layer of plastic cling wrap (Saran Wrap) on the area, I started at the bottom of the fenders and overlapped the layers as I went up.It sticks to the paint will keep any liquids off the paint. Then use a rubber backed thick bathroom rug over the cling wrap. It doesn't slide around and provides a good cushion to protect the bodywork and also it's more comfortable lean on while you are working. I tried it and when I was done the car looked like it had not been touched.