I have a couple of hints for you, but first, IMHO, Ultracote sucks. It shrinks better and is tougher, but the glue creeps. So I prefer Monokote.

When I covered the fuse on my cub I used one piece for the side up to the top of the cabin (even on the open structure behind the wing). I started by attaching the covering to the 1/4" inch stringer in the middle of the fuselage side. Then I stretched the covering to the bottom edge (in the middle) and applied heat. Next, while continuing to apply heat and tension (by pulling on the covering) I attached the covering to the bottom all the way to the tail and then to the nose of the plane. I repeated this procedure paying special attention to the area directly behind the wing for the top of the fuselage. Now comes the important part - don't trim the edges. If you've done this properly, you will already have a tight covering job because you were shrinking/tensioning as you went. But you may still have a few wrinkles to work out. You do this by applying heat to the edge near the wrinkle and pulling on the monokote. This is also how you cover rounded noses and wing tips. If you've already trimmed around then edges you can't grip the covering, but if you haven't then try this.