I spent some time with the Tventuring Under $50 DIY thread today.
If you take your trailer off-road, you may find that an ordinary ball-type coupler doesn't provide enough flexibility of movement for some terrain obs
tventuring.com
What a great design and write up! It is do-able for me although my MIG welder is only 140 vs his suggested 180 amp. If I have to, I could dust off the old Lincoln AC/DC Tombstone stick welder and see if that still works. I tallied up all the parts I would need from his material list (again, very nicely done) and now, 10+ years later, it is about $130 vs his original less than $50 but still way cheaper than the ready made options everyone identified.
Thank you all for your suggestions and comments. I do not have immediate plans to pull the trigger on this project but hope to by early spring. Will post back with my results.