Use large trash bags and put your floor mats into the bags. Tie the bag with and secure it under the seat so that the knot doesn't get under the pedals. The bigger the bag, the better.
When you get in/out of the car, lift the floor mat/bag out and shake it onto the salt. With this method, even if a few grains get under the floor mat/bag combo, it doesn't get ground in. Also, taking the floor mat out of the bag at the end of the week means that it will be as pristine as it was when you placed it in the bag.
The larger the bag the better, you can slide it up under the pedals and slip it under the door kick panels and maybe eve under the center console. The more you can cover, the less you will have to clean.
For the outside: Wash, wash and wash. Stay away from the salt that looks like mud, because it is. Don't follow closely behind a push vehicle or quad, moist/pasty salt will spray up on your hood, windshield, roof... just look at the push vehicles in the parking lot for this condition.
Be smart, treat it properly/like an adult and you probably won't have any issues.