Drove in the rain recently... it was extremely wet and caused a lot of road dirt and water to come up and around the seats, flooring and even into the footwells. Currently have the interior stripped and am deep cleaning. Also have purchased sound deadening sheets and tape with the dual goal of reducing sound / vibration as well as keeping water / debris out!
I live in a dirt track environment so my Moggies get very dusty just driving to the main roads, one trick I have done with the M3W is to use tubular insulating foam for 1/2 inch water pipes. It's very bendable and squishy getting right into crevices and other inaccessible areas sealing the gaps behind the seats and at the sides. The gap at the rear of the plastic boot tray where the leather strap is allows a huge amount of dust and dirt into the boot tray area, sealing that gap with tubular insulating foam makes a huge difference.
