I've cleaned mine with the spray foam upholstery cleaner that comes in a can. Also I've used my bissle green mean machine with carpet shampoo.

Since we've moved to a milder climate I haven't had the problem your talking about. Just vacumn and spot clean them now. When we lived in Michigan I started removing them in the winter and using the heavier clear vinyl mats during the winter months.

I live in the Northeast, with harsh winters. I can't wash my car mats easily in winter. I remove them and shake them out about once a month. I go to a professional carwash rarely (like once or twice a year) where they thoroughly vacuum.

In the winter, I soak them in the bathtub in hot water and detergent and oxyclean, then scrub with a brush and spray rinse them. Then I prop them up on the sides of the tub so that the water drains off them and they slowly dry.

I always threw them in my TL, cloth side out, with some old towels and rags. I really works well, then lay them in the sun to dry.

I always laid them on the driveway, dampened them a bit with the hose, sprinkled on some laundry detergent (or dripped, if you prefer liquid), then scrubbed all over with a stiff brush, finally rinsing thoroughly with a power washer.

I've used this method for 20+ years and it works very, very, very well. After drying they look new (excepting the wear spots from my heels).