Found this recipe on a PBS television cooking show, years ago and wouldn't fix my ham any other way since and when any of the clubs I belong to is serving Ham I'm always asked to do the cooking job.
half ham spiral-cut works without drying out
oven cooking bag
your favorite glaze
1Leave ham in sealed wrapping. Place ham in container of HOT tap water for 45 min.
2Drain off water, refill container with Hot tap water and leave in container an additional 45 min. The purpose of this is to even out the temperature of the ham so it doesn't overcook outside and cold in the middle. Overcooking is what dries out a spiral ham, especially.
3remove from water, take off packaging and the little plastic disk covering the bone.
4Place ham in an oven cooking bag cut side down. gather top, and tie cut slits near the top of the bag.
5place in baking pan. bake 1 hour in 275 degree oven (low) Meat thermometer should register 100 degrees.
6cut oven bag and roll down to expose ham. Brush with your favorite thick glaze. Boost oven heat to 350 degrees. return ham to oven about 10 minutes till glaze is sticky. remove from oven and brush again with glaze. tent with foil and let rest 15 min.
7My favorite glaze is made with Maple syrup and orange marmalade (combination of the two places I live)