Just my thoughts Robyn,but the only portion I would clamp,is where you have just ply seperation.You have to fill in the void,where you're missing wood, with either an epoxy or a mix of saw dust and wood glue,or a good wood filler..
The prep works is esential,and removing old gunk,and gluing clean areas,will assure a good long lasting repair.
If you were to clamp the areas where you had to fill in the void,the shell will collapes,squeze out all the filler,and become out of round.I would PM jccabinates and Purdie shuffle for their advise also.Good luck.
Steve B