I purchased a $5 round mirror at a flea market. I remove the crank on my jack. Slip a mirror holder over the post and see what I'm doing when I back up. Put the crank back on jack to lower trailer and it works great for me.
My concern with a back up camera, besides breaking it, is low light. I need to add light when it's dark to see my ball.
If you like, I'll post a pic.