[bigeasy1]

Being new to Seacrafts,i'm a little bit confused about the gap you're speaking about.Do you mean between the transom skin and the core? or between the edge of the core and hull bottom and sides?
I just finished removing the rotted core from the transom of my Tsunami,and also did it from the inside.
I have all the grinding,cleaning,and cutting done,and will soon be laying up a couple layers of 1708 on the inside of the transom skin,before i put the core(marine ply)in.
Was wondering what gap you were referring to.
I helped a few friends in the past on transom replacements,and we always filled any gap between the edge of the core and hull with filler.Never had any later problems,doing it that way.