John,
I was advised by SJSC to take my carbon seatpost out of the frame and clean any rust off once a month. I put a slice of inner tube over the joint between the frame and seatpost which helped by keeping rain out. This all worked well, but was a nuisance on a bike which is designed to be virtually maintenance free and I did notice small amounts of rust each month.
I did this for nearly a year before I decided to try some 'carbon grease'. In August I obtained a pot of Tacx Dynamic Assembly Compound Carbon and spread it inside the seat tube and on the seatpost before reinserting the seatpost without the inner tube cover over the joint. The paste has very small plastic balls suspended in it and these squash on tightening the clamp bolt, increasing the grip or allowing you to use less torque on the carbon component.
On reading your post I have just removed the seatpost to see what has happened in the last 4 months, answer nothing, the tube is not rusty and the carbon seatpost has not dissolved in any way.
Result one happy user of a carbon seatpost in a steel frame - thanks to carbon assembly paste - recommended.
