yes, those are decent, and yes they sell just the fork mount that is weldable or can be attached with a big u-bolt.
Another friend uses that setup with three of them bolted to a 2×6 laying in the back of his Suburban.
Yeah I see them all the time on the roof racks but I didn’t know if it made a difference with the bike mounted perpendicular to the travel of the vehicle. Just didn’t know if the starting/stopping would make the bike wobble and damage the forks. Hmmm