How about Flex-tape or Flex-seal spray? May not last forever, but it also may work. JB Weld also makes a special plastic version. Worked on patching an egg-sized hole in my LeatherLyke saddle bag. Twice. Yes, I had the misfortune of my bag coming off the holding stud due to overloading, and it rubbed through from the tire. I did have to make a curved mold from odds & ends to cover the hole temporarily while I built up the plastic epoxy layer by layer.I'm on it. Thanks!!