I had a utility trailer, and I used a mount similar to the one in your illustration to mount an optional spare to the A-Frame. But the added clutter on your A-Frame might be unwelcome when trying to deal with the battery, propane, and lift mechanism if you have a PUP.
My HW-277 has a spare mounted to the rear of the tub. Two through-bolts go through the back of the tub to hold the upper part of the spare mount, and the lower portion is attached with lag screws. I presume the tub was designed with this load in mind, because the tire is heavy and must shake like hell on rough roads.
A welder could fabricate a mount that tucks under the tub and attaches at the bottom to the frame, then comes out around the tub and attaches to the tub on the top with through bolts. I'd add "fender washers" or a steel strap inside the tub to reinforce the tub wall where the bolts penetrate. A similar arrangement could connect to the rear bumper on the bottom and the tub on the top.
I weigh 260 pounds, and I'm on that rear bumper regularly as a step to tuck canvass, install my cover, inspect caulking, and so on. The bumper shows no signs of struggle with my weight, so it's stronger than it looks.