In Germany there are police „special forces Carspotter“.
If they realize wrong tires, it isn‘t funny. Also the MOT would be a problem.
About the groundclearence I‘ve got a massive alloy shield from WOLF? fitted by BHM. But the most time I think the scratching noise is from the VERY long screws for the seatrails. And: the last time we travelled by P&O I think we hit something at the ferry with the rear valance.
This part:
https://www.wolfperformance.co.uk/product/trad-chassis-cross-member-rub-plate/Greets René