Assuming you have a cargo van.
In my 2016 LWB, I removed the mat covering the cargo area,exposing the area where the foot well would be for 2nd row seating.(search this site for descriptions)
After removing the filler pieces,you will see numerous threaded holes (aprox 5/16 or 3/8 but metric) that would be seat,seatbelt or tie down mounting points for 2nd row seats.
There are threaded holes on the B pillars(partition mounting points??) but I would be extremely hesitant to put any stress on an area that could affect door operation
Depending on the anticipated load,your bracket would have to incorporate multiple mounting points .
The cargo mat provides a lot of noise suppression so I installed a plywood floor over the mat.