After looking into it a bit more, the nutsert would have to be larger than M12 (M14? M16? The hole is 0.75" dia.), which is getting really big. After speaking with Rebel Off Road-Fort Worth, they suggested inserting a steal bar with a nut welded to it inside the frame over where the hole is...
I was replacing the skid plates on my '22 Rubicon with the Artec skid plates, and when I was removing the transfer case skid plate, one of the nuts inserted into the frame rail stripped out. I had to cut the bolt to remove the skid plate and now there's just a hole. It looks like a rivnut-type...
I have the same problem and came up with a variation of what's shown in this YouTube video: How to Load and Unload Your RTT Solo (Rooftop Tent). Quick and Easy - YouTube. I use a hand winch to crank the rig up to height, then slide the RTT onto the rack. Works pretty well!