Just to explain the "Drop outs"
When I had the bases of the rod holders for my boat lazer cut, I asked to get the disc that is "SCRAP" to them, back.
They refer to this disc as a "Drop out"
The end product...The 50mm pipe is hidden in the gunnel as well as the 6mm rod that us used to locate the rod's gimble at the bottom. This also prevents stuff falling into the gunnels.
Thought while at it also show the Bollards that I made. 3 of them. One for the stern and one each for the rear corners. Here I used the drop outs to cap the pipe.