I have an M100 and mounted a spare on the rear with a receiver cut in the rear frame member. The only problem is that you need weight in the front of the trailer or it tends to get out of control at speed. If I was to do it again I'd mount it up front.
I will back this up 100% as I did the same thing. Unloaded my trailer ran down the road 80 mph straight as a arrow. I put my 35" spare on the back of it and it was all over the road. Loaded it was ok, but empty and that was enough weight to unbalance it and drive me crazy. I am forchante enough to be able to run without a spare since the CJ and it share the same wheels and tires. But I'd much rather redesign it to balance it correctly.