I have begun a repair project on a boat. I am buying a 1970 Newman, tri-hull, from a friend, I got a great deal for the boat and motor(92 evinrude 48SPL). How ever the boat really needs some work. I had to cut out most of the middle of the floor deck due to soft spots and rotting. Once I removed it I found that all of the foam under it was water-logged and ruined so had to remove it also. I am unable to remove the beams that run the length of the boat, but did replace two of the width supports. I was going to add spacers to the beams to bring the floor up, due to the floor curve due to it being a tri-hull. Then lay down 1/2" - 3/4" plywood, spray expansion foam underneath, and then attempt to lay fiberglass on top to seal it in. Is this the right thing to do or am I putting more time and effort into this than I really should? Would I be better off saving the money and buy a new hull and put my motor on it?