I have installed the Shearwater fittings on a finished kayak and it was fairly simple.

A) Cut hole with a sharp hole drill
B) run string down through hole
C) Attach string to fitting
D) put epoxy on the part of the fitting that contacts the underside of deck
E) Pull string
F) adjust fitting orientation from "above" with pliers
G) use string to hold fitting in place while epoxy sets
H) apply finish to fitting

Easy!!

I hope this helps,
John VB