I smoke russets frequently with ribs, turkey, whatever. I find that medium size whole potatoes take 4-4.5 hours at 250 (temp for turkey). At 225, they get done the same time the ribs do in my #3.
Last weekend I did 2 turkey breasts and included 2 yams with the potatoes. I scrub the potatoes/yams with a stiff hand brush. Then I rub a light coating of butter on the skins, sprinkle a little salt, pepper, garlic and onion powder on. Then they go into the smoker bare as soon as I put the meat in. The yams were very tasty, skins had a good smoke flavor and the flesh was lightly flavored.