My spare tire came to me loose, so I've been looking for a way to mount it securely to the trailer. I noticed that others have mounted it to the rear bumper and I decided to follow this path. I made the mount from 1 1/2" square aluminum tubing with 1/8" wall thickness. I like aluminum because it is strong , light
and rustproof. It is also ridiculously expensive if you buy it at somewhere like Home Depot. I buy it from a local scrap dealer for $1 a pound. This mount cost me about $3 to make, including bolts.
You will note that the bottom of the mount has to be spaced out about 1/2" from the bumper to make the mount vertical. I used an aluminum spacer ring that I had acquired somewhere in the past. Bolts are 3/8" with nylock nuts. I also added a little foot at the bottom for the tire to sit on to distribute the weight
of the tire to one more point, in addition to the two mounting bolts. I used spacers inside the tubing so that when the bolts are tightened, they don't crush the tubing.