Well I doubt a 1.5"+ wide chain will fit through the space between the brake drum and the wheel rim. Anything narrower is too easy for the $40 universal "key" a.k.a. bolt cutters.
I found this:
Brinks 3020-057 Trailer Wheel Lock, J-Lock Style and I would throw away the cheap chinese disc lock, using an
ABUS 24IB/60 B KA All Weather Diskus instead. Has the same effect as the solution I listed above, provided the wheel can't be removed by removing the lugs. Probably not, but I will ask to be certain. If so I'd get one of those $20 lug nut lock sets. Total cost, $45.68.