A number of people have completely removed the seats, them removed the material/covers from the seats, and then recovered/reupholstered them. I just finished that job on my 'Hoe a couple of weeks ago. It's fairly simple. Washing your existing covers after they are off is easy but you don't want to use the washing machine.
Normally the covers are backed with sew foam (like 1/8" to 1/4" thick and somtimes covered with a backing fabric) and that wasn't meant to go through a washing machine. If there is no sew foam attached and its just fabric, you can run that through a washing machine if you want. Otherwise, get a big laundry basin and fill it with some woolite and warm water and wash them by hand and line dry them. That will get them way cleaner than anything else you would do with them on the seats and you won't have to worry about damaging their structure in a washing machine.
-B
