I would prebend. Resins do not like to be bent, whether they are polyester or epoxy. Life and ultimate will be sacrificed. I don't have small boat building experience, but as a commercial fisherman, I have done countless repairs, and have some experience helping boatbuilders finishing out both commercial and pleasure boats. Remember: Wood is bendable, it is one of the things that makes the medium a joy to work with: Fiberglass is a necessary evil, it does the job, but once wetted out and set, doesn't want any extra flex.