FF summed up the problem nicely. You want to prevent a side load on the threaded thru-hull fitting.
If I were installing one today, I'd use the Groco backing block bedded in epoxy and through bolted to the hull. I might use flat head machine screws instead of hex head if I wanted to keep the hull smooth, but like FF said, it really doesn't matter.
I'd use a Groco Flanged Adapter bedded in 5200 and bolted to the threaded inserts in the backing block.
Then I'd screw Groco ball valve onto the Flanged Adapter with a good bronze hose barb in the other end.
With a setup like that, the thru-hull fitting could rot away and you wouldn't even know it until the next time you inspected the bottom.