I found a design on the Pop up owners forum a while back.
No drilling into your roof, was attached with SS cable and some brackets.
I made mine out of like 2" aluminum C channel. Fits my mountain bike tires perfect as is, then I made some insets out of treated 2x4's
that fit my road bike tires.
The design is also good for lawn chairs etc if not hauling bikes.
I'd attach some pictures, but the new buyer just picked it up last night.
2016 Toyota Tundra SR5, 5.7 V8