I guess the fishing is just so different around here that it doesn't make any sense for me in my particular application to do something like this. Fishing in the Puget Sound regulates you to using one rod per person, so if you're fishing by yourself then you can only fish one rod, and if you've got 5-6 people total then you can only use 5-6 rods total. Of which for me, I've got the hardtop with 4 rod holders, the 4 plastic rod holders as the OP showed in his picture and then two on each side underneath the gunwales.....
The boat is a 99. I recently got my first GW last February, so spent the summer figuring it all out, replacing hoses, rewiring and cruising Catalina and the harbors.
Now I'm doing somemore tinkering with it during the offseason..
My original intention for the holders would be for trolling, along with the existing 4 gunnel holders and the Scotty downriggers. I was thinking it would provide a good spread of jigs to troll, with the two additions in the center.
You have a good point regarding the regulations, on the limit of rods per person and in the water...Same regulation here in So Cal......
I have the hardtop with the 4 holders across the top, with 4 recent SS clamp-on holders, 4 holders around the bait tank, and the existing gunnel holders, that is 16......should be plenty....
Placing some holders in the transom would provide moving the cleaning table (and BBQ) with a level-lock rod holder mounts, to the back of the boat. It currently uses the gunnel holder.
I might reconsider the 15 degree holders. This would be helpful is using as a flag pole or something....
Whether I want to build a table such as what Wxrhoon shows, well that is another topic....
I did get some confidence that the transom cap is plenty strong, with the plywood core, to put something through it...Properly sealed of course...
Thanks