Here’s a really simple-to-fabricate idea.
I don’t think everyone knows that there’s another T-slot on the UNDERside of the Beef Bars. I use the underside track for my solar setup.
So what you’d do is take a piece of aluminum angle or angle iron and cut the edges as pictured with a hacksaw or angle grinder. Then drill an oversize hole or make a slot to match up with the Beef Bar underslide T-slot. You make four of these for two panels. You can mount the panels to the angle with screws, clips, VHB, sikaflex, really anything.
You’ll need two screws and two T-nuts per bar, so 8 screws/8 T-nuts.
The best thing about using the hidden slot is that the top of the Beef Bars sits a little bit “proud” of your panels, so you can still store stuff on top and use the bars as intended.