I've got like 800 hours played, but I like to start over and over and explore. I kept seeing people posting like, "I can't find the trader…" but I've ALWAYS found him just by sailing in a spiral out from the center. Dozens of times, never too far away… until today.
I started over when the ice caves dropped, and I was hoping to play in this new world until Mistlands, staying close to the center of the map so as not to reveal any Mistlands biomes before the patch. But this damn trader! I'm so far out in my karve that I'm sure to stumble into a Mistland. So I cheat and use the seed viewer and sure enough, the nearest trader is like 4/5ths of the way to the edge of the map and right next to a Mistland. 🙁
So I apologize for thinking y'all were just doing it wrong. Some Trader seeds are trash. IMO his spawn should be refined to a donut x distance from spawn but no more than y distance out.