Hej Adrian, any roof bars that clamp onto rails will work from any car providing wide enough.
Locate a euro pallet out of light timber, industrial areas leave them out, ideally a double length X single width one , upside down on the roof bars, cable ties , your bags can sit in the cavities of the pallet and ratchet straps to the roof bars over a tarp if you must (gets noisey....) Two single light pallets on top of some fence pairings, screw /cable tie to make same as the double width.
Plastic pallets can be light ones too.
Or some planks instead of roof bars even....gaffer tape them to roof rails and add pallets. It's the ratchet straps that tie it all to the roof bars. Safe as....a Volvo!