I searched old threads and couldn't really find what I'm looking for. My son and I are tackling some gravel racing on a newly set up Salsa Powderkeg. We need to nail down a good transport system. I currently have Thule aero crossbars on my Toyota Landcruiser and have narrowed the rack options down to either the Rocky Mounts Tandem Mount R4 OR the ATOC Tandem Topper. Both look like they can be mounted on the Thule Aero bars. (unfortunately the Thule tandem mount is for round or square bars).

Can anyone with familiarity to one or both share your thoughts?

Thanks
Ben