There are multiple manufactures of air dryers and multiple models of them also. Look at the one mounted on your coach to see which air dryer it has, then google it.
NAPA Auto Part Stores also sell them, plus a lot of other HD truck parts.
Good Luck, Be Safe and Above All, Don't Forget To Have Fun
2006 Fleetwood Discovery 35H, 2014 Honda CR-V, M&G Engineering Braking System