Typically the number part relates to the length in some fashion, e.g. a 3000 might be 30 ft long (either overall length or length of the interior floor space). The letters usually designate a floor plan, e.g. CL might mean "Center Lounge" or something like that. But it could just as easily mean something else - marketing people are paid to be creative, so they are always changing things to fool us into thinking it's a new and improved thingie.
2004 American Tradition; 2014 Buick LaCRosse
Homebase in the Ocala Nat'l Forest near Ocala, FL