We have them in Ontario and the plate is attached to two plastic anchor thingys behind the front bumper.
I was suspicious my self that they will not last, but seem to be holding up fine.
If they strip out, I will put a strip of metal as a backing plate then use stainless hardware and some nylock nuts to eliminate the issue.
I added a plastic cover since the plate is held with just two screws at the top and the plate bent up on the hwy.
'00 XJ Sport, White - almost done for now...
'11 Town and Country - people mover :-(
'88 XJ Up Country, '01 XJ Sport, '08 KK Limited, '98 XJ Parts Donor, '07 XK Limited (the Stall-ander)