A couple of times a year I travel over to the Adirondacks where a buddy and myself troll from johnboats. Typically, I just lay my rod up against the back seat with reel on the floor while rowing. Of course one needs both hands to row. Over time this puts wear marks on your rod and real not mention the risk of having a big strike take your pole right out of the boat. In fact that happened one year to my buddy.
I'm thinking I could fashion some cutouts in a piece of PVC tube such that the rod is loaded with the real oriented horizontal initially. Once in place you slide the rod back, rotate it and slipping the real seat into another slot, eventually resting vertically, real down. Imagine the bolt action on a rifle. I'd have to clamp the holder to the boat holding it at a 45 degree angle somehow. However, his arrangement may hinder quick removal of the rod from the holder during the calamity of a strike and run.
Y'all got any designs/ideas?

Theres a gazillion of them on line. Why reinvent the wheel unless you just like to create and tinker.

I'd made many of them for use on a kayak. Some tubing either PVC or ABS, or even tubes from a vacuum cleaner end piece or plastic shelving uprights, will work. You need to slot the tube so that the reel can pass and make the slot long enough that the rod goes in at least to the last inch of the grip. The slot should only be so wide as to pass the reel foot.

There are numerous commercially made rod holders you can mount to your canoe and then slide this pipe into. It ends up being a two-part affair but works very well and is easy on your fly rods.

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Scotty makes one that fits their existing mounts.

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Indeed there are a ton of commercial "spinning rod" holders that won't work with fly rods whereby there is very little shaft beyond the real.
I did find a commercial fly rod holder - $350.00
BTW, why make a fly rod for that matter....geesh?
Scotty makes a holder for $27;00 that looks great accept you need to screw it down.
Anyway, I was thinking there might be folks here in the same boat, excuse the pun, that have come up with something cheap and durable and doesn't have to be permanently mounted.
Though, I imagine 95% of you don't troll in a borrowed row boat.

Search for a holder that you can cut up and modify for your specific use.

Necessity is the mother of invention, invent something. Lol