Since the RV is 15 years old, perhaps one of the A/C units has been changed out. Best way to find the answer to your question is go up on the roof and remove the cover and look for name, numbers. While there, you can measure the covers and order replacements. Also might be a good time to clean them.
Bob & Donna
'98 Gulf Stream Sun Voyager DP being pushed by a '00 Beetle TDI