Flat Mounting RTT?

So I've got an ARE Overlander shell with roof rails running down it. It has Yakima Round Crossbars on it that mount to two T-Slot nuts on each tower for a total of 8 nuts in the roof rails. My question is can I mount an RTT to those T slot nuts in the roof rails? Mounting a tent on the crossbars with U bolts would be easy, but would put it 4-5 inches off my topper and I'd like it to be closer to the shell.

I'm liking this flat mount here (https://forum.gofastcampers.com/t/gfc-rtt-mounting-to-a-cap/2756) but can't find the products he used to mount them? Anyone know how that's done? Would appreciate a link to the product on GFC website if I'm dumb and missing it. Thank you

 

https://gofastcampers.com/products/aftermarket-rack-mount-kit?variant=3126971006986
Or you could have a local fab shop bend some hat rail up for you. Lots of ways to mount a RTT low.