I use signs as well, however, I took the time and researched plastic manufacturers around me and found a place 45 min away from me that sold me a 4ft by 8ft sheet of white 1mm thick for $17. I just rolled it up and put it in the car and have been using that sheet for over a year! They have all kinds of stuff in different thicknesses from clear, aluminum coated, corrugated, etc. My point is to look for these types of places near your residence....you never know!