I use a Master locking pin for my tongue. Has been fine for about 5 years now. Has a weather cover that works pretty good, just make sure it is oriented so that it doesn't become a cup to hold water in. I give the keyway a shot of silicone spray once a year.
https://www.amazon.ca/Master-Lock-28...7145804&sr=8-2
My main security is a wheel lock like this:
https://www.amazon.ca/Anti-Theft-Par...145684&sr=8-10
I've been using this for about 3 years. I park in a yard out around Navan. Very happy with the security, but you can't be too careful and it is a very visible deterrent. Mine was a Prime Days deal, not quite so expensive (not that this one is outrageous).
Someone might point out that you only need to replace the wheel to steal the trailer, bur really, who's going to bother? The objective is to tell them to move on to an easier mark. If they want it that bad, they'll get it no matter what, and frankly if they want it that bad, they're looking for something bigger than an X-Series trailer.
ETA: And, oh yeah! Welcome to JOF neighbour! (you should appreciate the spelling
)