Is it possible to mount any of these tents onto the factory crossbars? In other words, do the tents have their own flat sleeping floor support, or is that what the flat roof rack is for?
What combination set-ups is everyone running?
Yes they have their own flat floors that fold out when opened. However, the factory roof rack on a 4Runner (I have a 2016 SR5) is not rated to hold these tents generally. So i have upgraded to an WTS ARB ROOF RACK BASKET 70 X 44 INCH (3813010M) You can get crossmember types from Thule, etc. However with mounting kits, etc they seem to be over $1000 and this rack is max $1400 new. So why not go with a full basket that has multiple uses vs a basic rack?
You will need the rack + mounting bracketrs for your Runner + RTT + Mounting hardware for your rack. Not sure if it is specific to the rack or not.