1999 TM sl 2720

Looking at a pre owned unit. Any insights into the 1999 vintage. Did they have any problems in those years. The floorplan still looks identical to the new ones. This one has a wall air conditioner. Was that stock for the year or would it be an aftermarket. How about sealing of walls and lift mechanisms. Have they been the same all along. Any input greatly appreciated to help me make a decision.