Jim, I would come out what ever the need is to cover the tire, and run a sheet of aluminum from in front of the fender nub to the back, just cutting out the high part, with a angled rail along the edge, so you could use it to carry stuff on. It should look planned it would seem. Take a look at my build and imagine the expanded metal being solid. I think tha would work.
I agree you need to go wider on the axle if you are having problems with off camber stuff. The wider the base the better for that stuff for sure. We all have made our first trailer and learned from them, you sir have built your first trailer and we are all learning from you. Such a great design, quality, craftmanship. You might want to finish this puppy up and make as stable as you can and sell it. You know what to do different now. Fantastic build though. Hopefully what we have suggested will cure the problem.