front derailleur mounting
 

Should the seat tube where a clamp-on front derailleur is mounted be protected in some way before the derailleur is mounted? It seems like otherwise the clamp will scratch the tube. Is there some preferred way to do this?

You have to balance clamping tension versus risk of sliding down the tube
(or if overly vigorous with the 5mm allen wrench, as I was ~'70, and breaking
the clamp on a Campy NR FD). A wrap of teflon pipe tape under the clamp
or something similar in plastic will provide some protection against paint damage
but nothing very thick or slide down is likely to worsen. I have a roll of 1.5" wide
TFE transparent film about 5 thou thick I occasionally use. Thick enough to
provide some protection to the paint but not so thick as to be problematic, so
far. Character of the paint is a factor, some is pretty soft, some, like powder
coat, very tough.

Just mount it on the paint. If you do it right, you shouldn't have to move it again.