You say you can use a shovel, but worst case scenario, how do you feel about shovelling 20 tons off the back?
I tend to agree, containers are a good idea. I had a job once driving a class 2 for a local library. No lifting whatsoever, easy work. The point is that there are many jobs out there. If I were in your position, I would go to driver hire (or another driving agency) be honest about your disability, and do a variety of jobs for a while until you find your niche. There are jobs out there that you have not even thought of, and many suitable jobs we can’t even name.