here's some info from the FMCA: (who and how much is an inspection?)
How Old Are Your Tires?
Molded into the sidewall of every tire manufactured is a code that indicates when and where the tire was manufactured. This code is required by the United States Department of Transportation, and the identification number starts with the letters ?DOT.? The two digits following the letters DOT indicate the plant where the tire was made. The last group of numbers ? a four-digit code ? is the one that discloses the week and year of manufacture. The weeks of the year are numbered consecutively, and the last two digits of the year are included. So, for instance, the code 4711 indicates that the tire was manufactured during the 47th week of 2011, specifically, the week of November 21.
This information is especially important for the owners of motorhomes. Motorhomes aren?t always driven as many miles as the typical passenger car, so motorhome tires often wear out as a result of age-related issues rather than mileage. Because so many variables are involved, it is not possible to provide a replacement date based simply on the calendar. So, motorhome owners need to keep their tires properly inflated and also have them inspected regularly by a tire professional, such as a dealer. Once a motorhome tire reaches 5 years of age, it should be inspected at least once a year by a tire professional for signs of wear and aging that would indicate the need for replacement. Most motorhome tires will need to be replaced before they reach 10 years from the date of manufacture, but, if not, they definitely should be replaced at this point as a safety rule, even if they still appear to be serviceable.