This is a major job, which will mean removing and replacing the entire deck This will not only be time-consuming but also very expensive, and keep the boat out of the water for a long time. Sourced from: http://www.doityourself.com/stry/7-signs-its-time-to-fix-your-boat-stringers#b
Fiberglass in the boat can break but this should not be disheartening since this is a material that can be repaired easily.
Very little finish work will be required. Sourced from: http://www.boatus.com/boattech/casey/fiberglass-repair.asp
So you will have eight contact points on an 20-Ft boat. Sourced from: http://www.customboatrepairs.com/jmla/index.php?option=com_content&view=article&id=69:how-to-remove-a-boat-from-a-trailer&catid=3:diy-tips&Itemid=17