My Overnighter was pretty bad inside too with a lot of black mildew into the carpet.
I cleaned it with the upholstery wand on our Bissell carpet cleaner. Used a mix of hot water, carpet shampoo and oxyclean.
It came up like new and has stayed that way.
You can do the same thing with the mix in a bucket with a hand scrub brush and use a wet/dry shopvac to pull it back out of the carpet which is basically all the Bissell is.