The best I’ve seen/used. https://infiniterule.com/
Not cheap but imo worth every penny. I got the 3 pack #61633 ($185) – Trailer Tongue lock, Coupler lock, Hitch pin lock ALL keyed the same (6 keys total). And 2 other coupler locks. BUT the last I will ever buy. Plus you can order next year and get the same key. They even make one for the Demco coupler on my Aluma trailer. Stainless steel and made in USA. Highly recommend.
Oil collects dirt. They recommend 3-in-One Lock Dry Lube. $5 at L&M.