I welded one up for the Montero this past year. It's designed to accommodate plastic poultry flooring if I want to have a solid platform for photography, air shows, etc. The cross bars are heavy-wall electrical conduit. There's almost no deflection at all walking on them.
I removed the factory cargo rails and created a low-profile mounting rail system from aluminum channel.
I welded mounting feet to the rack, each having two bolts that secure it to the tracks. It pops on and off in 5 minutes.
It's very stout without being ridiculously heavy. I built it short to allow full access to the Montero's enormous sunroof, but the tracks extend all the way forward so that a front crossbar could easily be mounted if the need arises.