Not sure why you have 4 layers of glass there but here is what I would do:  (1) sand back from the 4 edges of the fin box say 2" With 4 layers you can be pretty agressive sanding into that 4 layer (2) after you have the box installed with fillets and glass on the inside apply a layer of glass or better yet 2" cloth tape around the edges of the box.  (3) after that hardens use sandpaper to fair the edge into the hull.  Then fill out the weave with epoxy.   Just be careful to make sure that you don't drip a bunch of epoxy done into the fin box.   Your idea of extending the keel strip back over the edges of the box is also fine  The strength of the installation comes from the inside.  All you really want to do is thoroughly seal the joint betweent the fin box and the hull.  You could probably skip all of the above and just fill the joint with a thick epoxy layer.  When I install fin boxes I always install some sort of physical structure that keeps the box vertical during the installation process as well as providing support in case you ever hit the extended fin from the side.   

  Thanks, the 4 layers are the full wrap, the bottom piece and 2 layers staggered 3" and 2" cloth tape 

Hi DL, 

i have installed skegs in a lot of kayaks and also paddle them a lot.

i am very attentive to all the interior work you have mentioned.  

before the new box goes in, I always ensure i have painted the exposed wood (due to the cutout) with epoxy and after the box goes in, i am careful to ensure there is no crack or void for water to get between the outside of the box and the hull.  but no further glass work.  i do mask the box interior and do a final coat or two of plain epoxy on the outside of the hull as part of the process so the epoxy spans the hull and the exposed edge of the fin box....but agian, no further glass work.

i have not had any problem with delamination and i have 10 years plus on several of the boats with skegs.

protecting the bottom of the hull with extra layers of glass as you did or with a rub strip is always a good idea and i do that as well.  my sense is delamination is going to be more related by good glass work in the first place (fully wetted out and no voids), preventing water intrusion, storing the boat clean ad dry,  and avoiding damage that goes unrepaired before going in the water again.

h