The last time I used a stiff scrub brush, a little bit of Oxy Clean powder, and the garden hose.
Both work well, but the power sprayer is less work. Also, as mentioned in an earlier post, use the widest angle tip you have so you don't damage the carpet.
I had a carpet cleaning place at the house, and flipped the guy $25 to do the boat. It was ok, but my way was more effective.
Wish I could get the light gray vinyl clean as it should be.