I've mainly done it on paperback cookery books which had broken up because they were both quite thick and always used flat. In most cases the spine cover has been badly worn and the book broken into sections. I've generally made a new spine cover out of thick brown paper and then clamped the book at the spine between two pieces of wood. Allow the gun to get fully up to temperature and then cover the spine with a fairly generous film of adhesive and stick the brown paper on with an allowance of about an inch either side. Leave about
10 mins, remove the clamp and stick the excess brown paper down on the front and back covers (or cut it off). On one I got interrupted and the hot melt glue set before I'd fixed the paper down properly - a quick run over with a hot iron (standard ironing type iron) fixed it all up.