I'm assuming they're fabric seats, not vinyl or leather? Assuming they're fabric, I clean the fabric seats in my cars. I rent the carpet machine from the local grocery store, Home Depot, Lowes, etc. It's usually about a $20 rental and comes with an upholstery tool. It squirts the cleaning solution on, you can use the tool or a hand brush to scrub it all down, then most importantly the tool extracts all the dirty water, dirt, soap etc out. The seats will be clean and damp when done, and usually dry easily overnight in average conditions.
If you don't have access to one of these machines or don't want to spend the $20, you can always deep clean with an appropriate soap and lots of water, then use a wet/dry vac to extract all the water, soap and dirt. I have done that as well, and it also works great.
2005 Newmar Mountain Aire 4304 - 4 slides
2011 Jeep Liberty 4X4 towed