I had a play today with my new Thule footpack and fitting kit for my roof bars . Thule Evo Flush Rail 710600 with fitting kit 186009, the footpack will fit all Thule roof bars including the square bars.
Roof box is a VW 340 litre very lightweight at only 13kg and takes a capacity of 50kg, roof weight capacity is 75kg.
When the weather improves in a few months I will be fitting my Autohome rooftop tent for a camping trip. I will be interested to see how much either of them will have on mile per kWh.