I always apply a liberal coating of Copper Ease anti-seize compound to the inside of the frame, and the post itself, when fitting a seatpost to all my bikes.
Every couple of months (or in winter, each month) out comes the post, it gets cleaned and Copper Ease re-applied, and then refitted.
Never had one stick (fingers crossed!) and any residue that weeps out is easily removed with a cloth. I use the Halfords own-brand Copper Ease, it's really cheap and does the job (and smells lovely, too!)