Hi. My project Spider ('78) has a tan canvas top which has some discoloration and light stains on it. I think there is old mildew there. Also, it seems too porous, so I was hoping to find a product that will clean it well and then seal it. I've already tried simple green and a brush to clean it, but I'd like to get it as clean as possible before I reseal it. Personal experience, anyone? TIA, Patrick