Floor tie in

[Cheg]

I need some feed back on how to tie the back of the boat including the fish box with the floor


The pic shows the back of the boat suspended 6". The narrow strip along the back of the floor will be tied into the floor with epoxy and fiberglass. It will help support the fish box and also channel water out 2" drains that havn't been drilled through the transom yet. The question is, do I tie the fish box in with fiberglass or have it sit on a small bead of 5200? How much flex is back there? Will a fiberglass tie in self destruct over time from stress? Will using 5200 give it some "give". Along the back sides, I was planning on tieing in with fiberglass. I hope the picture is good enough. Thankyou.
Cheg