I believe it would cost you less to just have the seats recovered when you consider material, time and labor to paint or stain them. I am not sure of your area but I live in Ft. Lauderdale, a heavy boating area, and there are affordable (cheap) boat upholstery places all over the place. Some will even drive their van to your boat and do the work on the spot. If you want to save some money unbolt all the seats, panels and bolsters and take them into the shop. It is usually just a few screws holding everything in. While you have it all out it would also be very easy to replace any carpeting and check the flooring for weak spots.