hi m8
i had a kangoo 53 plate with 3mtr pipe on top and never had any problems in fact one very very windy day the pipe actually saved my life.
i was driving down dual carriage way with a large window company van in front when his triple extending ladders flew from the roof of his van and headed for me like a arrow rather than coming through the windscreen and taking my head off they hit the pipe instead.
they did bend the pipe down and smash the windscreen,dent bonnet etc but hey i,m still here.