Writeup here:
Cheapest DIY Heavy duty Roof Rack Crossbars for the GX460
These are just attached to the factory rails with factory style clamps.
With 4 per side now it would be stronger than the factory two bars but RTT need static and dynamic loading strength. Not sure.
There are thicker bars that can be used that will definitely not deflect at all but I chose the slimmer, about 1" tall.
These deflect a little when I span end to end and stand 185lb on the center. I'm sure these would be fine with the static load, especially multiple bars but I have no idea on the clamping strength/safety.
Edit- Actually these are basically the same design as the LFD bars, just a lower profile, and they seem to work for folks with RTT just fine. LFD just J-clamps to the factory bars as well.
So basically, I'd say yes. If you use full size superstrut, there's no deflection at all. You could also use the larger hardware. The curled edge of the superstrut makes a perfect J-clamp. No need to spend $100 on each bar.