Question is: What are the best tried and true methods of installing deck fittings?

There are a lot of options for deck lines. The Maroske fitting system is nice and clean, but some people may find it a lot of work. The simplest system I've found is simple loops of webbing bolted through the deck. This is low profile, easy, secure and clean.
I use a finish washer on the outside and and a somewhat oversized washer on the inside. Melt holes through the webbing with a soldering iron.

It is easy to add more later if you want, and if you don't like the ones you have, it is a small hole to patch.