Steven, what is the material on the chimney now? How is it flashed? Remember with siding to not over drive the nails to tight to the wall. Place the nail in the center of the slot, use galvanized roofing nails and when your siding is installed you should be able to slide the siding against the wall. You have to allow for movement as the siding expands when the temp changes. Use "J" chanel along the roof slope and manufactured corners. Make sure the cap extends down over your new siding and be careful working up in the air.