I just want to know why you didn´t use balsa for '' filling'' the space in the vertical stab between the rear fuse and vertical stab and you use light filler? Maybe the balsa save you some weight...
rather than using filler for the fairing on the fin I would have used balsa block profiled to the fin and then sanded to shape as you did with the filler. Then you could have removed the balsa block and hollowed in out more.
The two steps here were; first use the fin to cast a thin fiberglass shell that would become the inside surface of the fairing-second, build up the fairing to match the contour of the turtle deck. I used the lightweight filler for this because it is very easy to shape, and it becomes pretty hard when you apply resin and fiberglass.
This is not the actual turtle deck that will go on the flying model. It weighs about four pounds so far. It is a plug that will be used to make a female mold (mould for our friends across the pond)
Thanks for the comments I hope to have more pictures up by tomorrow that will make it clearer what I am doing.