Success!

Let’s hear it for Dremel cutoff discs and sledgehammers.  A powerful combination.

The only problem was access–getting the cutoff disc to the shaft of the lock.  Cutting off the rubber grip did the trick.

At that point I could get at the shaft and things went fairly quickly.  Only took a total of three discs–one for the rubber and two for the shaft–and one final whack from the sledgehammer, and off it fell.

Next step–tow the trailer out of the garage and clean it up.