Jbob Ah, it’s a threaded flange that uses bolts, the same setup my dinky little 70’s boat trailer uses; You might be able to find a padlock with a shackle that can pass through the bolt hole and around the outside of the hub, the thing is most people know that if you just smash them hard enough they can open. Populating all the holes might slow them down a bit especially if the lock is behind the flange hub, but its also a PITA to get the key in blindly.
Could just remove the entire hub, to replace it the thief would need the wheel & tire, bolds, wheel hub, seal bearings, castle nut and harpin, plus grease if they want to get any distance, but its work to put that all back on, check and adjust the loading on the bearing.
Since its parked someplace can a ground bolt be installed, something you can loop through and run heavy chain from it around the axle and other non-removable trailer parts?