Why not roof mount.. A lot easier and can get plenty of bikes up there. I have an A4 Avant too. Love it, what a workhorse
ou will need a ladder. we use roof bars and a roof box on longer camping trips and with the box mounted slider IDE of the bus I can get to it by standing in the open slider doorway and holding onto the roof bar with one hand. No chance I could put a bike up there or get it down and I'm 6 foot 1"