I had to do this on me KIT Companion TT , I welded two brackets on the bottom of the frame rails and then a 2" square tube with a 2" receiver hitch in the middle of the cross bar and one off to the side for the spare tire mount.
So basically nothing mounted to the bumper. That because on my first TT with the spare tire and 3 bike the bumper cracked around both frame welds and the bikes were bouncing down hitting the freeway when someone pulled up along side of me pointing back.
You can also position the bike receiver off the the right just enough the the bikes don't block your tail lights, and the tire receiver off to the left just enough to not block those light.
You can pin the cap so you don't loose it but that won't help when you hang the bikes on there and loose the whole thing. "Like I almost did"
This is the new hitch I put on my Landmark for our bike but basically the same thing you need.
https://heartlandowners.org/showthread.php/54076-Project-LM-365?p=439083&viewfull=1#post439083
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