First, it is important to understand that changes did not always occur on model-year boundaries, as they tend to do with cars. Many of them occur during a model year. And they do not always occur on all models at the same time. So in 2002, for instance, some TMs had the air conditioner on the front roof, and some had it on the rear roof. And within that, some 2720SLs had it one way, and some 2720SLs had it the other. And some still had the air conditioner in a kitchen cabinet.
So you can't say that Feature X appeared in the 2002 models, but was not in the 2001 models. However, once a change was made, it tended to crystallize very quickly.
My first TM was a 2002 2720SL. I seem to recall that 2001-2002 was a time of many changes, some minor and some more major. By 2004, things had settled down, and since then, changes have been more incremental. I think of the following changes that occured more or less in that time frame.
- Rounded wheel wells introduced
- Spare tire moved from rear bumper to the underneath location
- Air conditioner placement
- Wood framing in the shells replaced with aluminum
- Horizontal propane tanks introduced on the slideout models
- Front cubbyhole removed from the slideout models.
Of course there were others, and I'm sure that some owners will suggest different dates for these.
Just my memory ... others will chime in.
Bill