Because of this, I use an old stock pot for my canning.
The key to BWBing is to keep the jars off of the bottom of the pot to prevent scorching, for at least one reason. Anything you can find that will keep them off of the bottom will work fine. I used to simply use a wadded up towel in the bottom, but that makes a total mess. I realized that if I tool all of the jar lids from the gallon jars that busted in the garage when a shelf fell earlier this summer, that they fit beautifully in the bottom of the pot. I tied them together with a bit of wire to keep them in place and make the contraption heavy enough to stay submerged.
See how neatly they fit in the pot! I can fit five pint jars, four on the edges and one in the middle. It's a snug fit, but they all sit on the bottom nicely. It can fit more half pints, but the problem with those is getting them to stand upright since their bases are a bit smaller than those rings so they sit awkwardly, but if you have enough of them, they can support each other.
EG, I know you're the fabrication man and can most certainly do better than this with your set up, but hopefully the idea will help.