We use 4 of these plastic wheel chocks on the front and back of each wheel. I called Camco Tech Service (camco.net) about the Expiration Date on 6/26/2019. The plastic lasts 4 year and then you need to replace them. This is not only due to UV exposure but due to plastic aging. The expiration date (not mfg date) which is stamped on the chock is often wrong since the factory does not bother to make sure it is set to 4 years later. From the date you purchase them new, you need to record your own expiration date 4 years later. Camco has "gone around and around" with the manufacturer and can't get them to change the expiration date to the correct date in the future.