hidden problems, HELP!

[salvagefirst]

purchased a 1989 23cc last june, looked around the boat shows and decided to replace the 200 merc with a 250 suzi or E-tec carried the boat to a repair shop they said the transom seems solid that he wouldnt be afraid to hang a 4 stroke on it.so i am calling around trying to get the best deal possible, while im waiting, i ll just fix that little soft spot between my console and leaning post,now i have found a bad tank, rotten tank support left stringer loose from the hull and the foam wet in the bottem of both stringers.First question,where would you cut the floor out for stringer repair, What weight fiberglass and type of epoxy to fasten the stringers,i plan on building a new fuel tank deck and using strips with 5200, The foam seams to be what killed it the first time and will the stringers dry out or do i need to remove the foam and refoam them any info would be very helpful