Off road + boxes = tears.
Always
not correct.
Many, many riders use TOP boxes off-road - Motorradical, BMW OEM (aluminium boxes), etc.
they have
stainless steel racks, with
stainless steel bobbins, and are well capable of serious off-road work, when not over-loaded.
Have a customer (and off-road tour operator) who does in excess of off-road 20,000 km per year - no problem whatsoever.
Plastic boxes have no place off-road.
Cheers
Chris