How much would a roof box affect the performance of my orbitor antenna. The antenna is located on the roof towards the back of the vehicle and the roof box is...well on the roof !
Iv'e used a roof box next to my Antenna in the past, on a magmount near the back of the car and I found the S.W.R. was hardly affected at all, so you should be ok.
I have a Wilson 1000 (drilled thru roof mount) right next to the roofbox on my Ford Ka. The antenna sits about 13" away from the edge of the box. I checked the SWR before and after, and only had a 0:2 difference.
I think that might change radically if I were to start carrying metal items in the box, but as it is now, it is OK.