Cleaning seat fabric

Take the covers off. If you can afford it, have them dry cleaned. They will usually be able to get stains out. If not dry cleaning, pre-treat any spots, then fill your tub about half full of cool water and laundry detergent. Lay the covers in the tub ad push them up and down enough times to have the water circulate through all the covers. Let them sit for 10-15 minutes. Repeat three or four times. Empty the tub and refill with cold water. Do the pressing thing again, drain and. Refill the tub and repeat at least one more time. Any detergent remaining in the fabric may cause it to soil more quickly.

This is also a good time to check the seams and make repairs if needed. Also a good time to air out the cushions themselves. Sprinkling them with baking soda and letting them sit outside for a few days should help a lot.

Good luck!

I would guess the mice made nests inside the seats. Get the covers off and clean out the mouse stuff.

You may have to paint the springs and framing to lock in the smell. I would also guess the smell will not come out of the foam, batting and fabric depending on how bad the mice nests are.

Has anyone ever tried using an ozone generator to remove smells in a camper?

I agree with Hamlet, I've done this on several vehicles I've bought from my brother who always hauls a big dog around.  Laundry detergent does wonders.  Washing cloth is washing cloth more or less.  I do this to the seat covers, pull the carpet out and lay it on the driveway, scrub and hose it down with the same solution.

On the cushions, I've had some ideas rolling around in my head (scary) but haven't tried them yet.  I too have some foam cushions that I would like to re-use but have that "old camper" smell.
My thoughts:
1) Mix up a strong mixture of you favorite good smelling laundry soap and water in a large tub, barrel, bath tub, you know, enough to cover the cushions. 
2) Place the cushions in one at a time and "walk on them", kind of like stomping grapes so that the soap solution gets into it.
3) Probably follow with a rinse cycle and/or use some fabric softener for added pleasant smells.
4) Now, how to get all that water out before it causes problems, hmmm.  Stepping on them to squish it out might work a little?  Jack up a vehicle, place a piece of plywood on top of the foam under the tire and let it down?  Might squeeze out quite a bit?  Or just hang up in the tree to drain for a few days?
5) Last thought to thoroughly dry them out after draining; put them in the hot, dry attic for a couple weeks?

Like I always say, It's just a thought, didn't say it was a good one...

We had a 1974 trailer that smelled like someone had lived and died in it. I tried the ozone machine, tried nil odor, tried air freshener, dryer sheets and coffee spread everywhere. there was no foam cushions in the trailer. it turned out to be rotted plywood under the water tank. The wood was dry but it still smelled bad. Once that was replaced no more smell.