I'm in the process of putting a TBS single seat / cowl on my 2002 TB.
(I have the added problem of having to add a seat lock mechanism to my bike.)
The TBS frame and the TB frame are not the same under the seat. The TBS frame is a bit higher than the TB frame. Therefore the rubber bumpers on the underside of the TBS seat don’t sit on the TB frame.
Underneath I'm using some rubber replacement chair leg tips that I found at Home Depot
(like these
http://www.robertbrooke.com/chairgli...chairtips.html )
They slip right over the rubber bumpers on the TBS single seat to make up the difference between the TBS seat and the TB frame.
Also note that Triumph ships the actual cowl separately from the seat. A neat little note accompanies the two parts and says something like “Cowl must be installed by professional Triumph mechanic.” After trying to fit the two parts together I begin to see why – they don’t exactly mate (and overly forcing the plastic cowl to conform to the bolt holes doesn’t seem too wise). I had to drill the rear bolt hole slightly to one side (but it is covered by the top of the hex head bolt) in order to secure the cowl. I did not crank down on any of the bolts, but I'll hit them with some lock-tight.
I’ll try to get some photos done soon of all mods for Triumphrat.net.