If someone has factory crossbars installed, could you measure the dimension, front to back? Or if you don't have crossbars, could you measure the outter-most plugged holes for the crossbars? That should be close enough. With my Santa Fe, I had to pry the cargo box clamps around the bars because they were so far apart. My cargo box's clamps max reach is 38.5".
Installed the cargo box tonight. Fitment is the exact same from the 3rd gen. Didn't have to move the locking mechanism inside the box. Tailgate is all the way up and box does not touch. About 1/2 cm clearance.