Find a butt bar design you like, take photos, measurements, get the local welding shop to make them up for you. We have heavy pipe, 3inches wide, with a drop pin on one end, link to wall plate on the divider. Our large horses can sit on the bar, doesn’t bend or give. Not draft sized, but one horse is up over 1500#. I like this particular design, but you might like another design better. Husband can weld, so he fabricated these up from his scrap metal pile, installed them in the trailer. A good local welding shop can make up whatever you want, probably not terribly expensive either.
I hate the chains, never heavy enough, easy to get pinched in, swing too freely during loading and unloading to suit me, while this single link on our butt bar works well and is restricted while hanging down free. Pipe is wide, no creases in their rumps, metal is smooth too. I don’t use padding, no one gets any rub marks with such a big diameter pipe behind them.