I don't have good crisp answers for you, but here is some help.
Ford has produced the F53 RV chassis for many, many years, going back at least to 1989. There were motorhomes on Fords before then, but I don't know if there was a specific designation for a motorhome chassis, i.e. te F53. The F53 has gone through at least a couple iterations since then, with beefier frame rails, bigger engines, stronger transmissions, etc.
Workhorse Custom Chassis was formed in 1999, buying Chevrolet's Rv & commercial van chassis business. They were manufacturung the P30/P32 Rv chassis at the time and immediately set about improving the P series and also developing the new W series from the ground up. I think the first W20/W22 came out some time in early 2001 and was in full scale production later that year.
2004 American Tradition; 2013 Buick Verano
Homebase in the Ocala Nat'l Forest near Ocala, FL