Alrighty, here's my $11 DIY solution to adding a rod holder to my 2010 Hobie Oasis (which doesn't come with rod holds like newer models do)
$7 heavy duty plastic rod holder from tackle store.
$4 7/8" dowel rod and bolt.
Dowel slides easily into 7/8ths" sail mast hole. Rod holder easily swivels on a single bolt holding it to the dowel, and swivels/turns to a variety of positions. I can position it for trolling or for stowing the rod, and take it out when not needed.
I added a small bungee to provide tension on the bottom of the rod holder. Helps keep the rod tip up. The bungee clips to the stock round cleat mounted below the mast hole.
I looked at the store-bought mounts and the Scot in me didn't want to spend $50+ on a ball mount and adjustable Rod holder. For something I would only occasionally use. I only fish from my kayak every so often. Plus, like many here, I get perverse joy from MacGyvering up things like this.
Update:
After a few trips I ended up modifying this jerry-rig holder. I added pvc pipe to top of the dowel to move the holder across into the forward seat area then angled left to get holder out of the way of my peddles and leave forward seat open for my tackle box.