I've done SUP fishing with my SB super fish 9'8", like you I did put a fish crate and plumbing plastic pipe fixed on the mast plug nut.
Now I use a kayak , last night I took the first wahoo of my fishing life

So, by the time I was doing SUP fishing, I did think about ( but not made) fixing the winch and a single ring on the the top of the shaft and use the paddle as a rod