My .02 regarding seat cleaning. We have all seen mold and mildew on seats. We all know it is a pain to get rid of. I think bleach is an essential step as it is a biocide and kills any living "thing" in relatively small quantities, yes, even humans. There is a reason they don't use chlorine gas to treat swimming pools like they used to back in the early to mid 1900.
After the bleach application, there may be staining left. There are a wide variety of products to use, but they all have their own drawbacks. Murphy oil soap is great, but you want to ensure compatibility with the vinyl on your boat as it can cause discoloration and staining. All other methods can be used and depending on the severity of the staining, abrasives such as magic erasers can be effective, but damaging on a small level. Whatever you use to get rid of the staining is going to be damaging on a small level. The trick is to use preventative maintenance to not have to use that same method frequently.
Do whatever works best for you with the physical capabilities and time restraints that you have. After it is clean, put 303 on it as a preventative measure, also helps restore some of the luster of the vinyl. Develop a regular regimine for preventative maintenance. For me, about every 2 weeks my pontoon vinyl gets treated. I usually look for rain in the forecast, mix up about 2 oz of chlorine in a 2 gallon sprayer, soak the vinyl and carpet down with the mixture about an hour before the rain hits, rain rinses it away. When dry, 2-3x per year, it gets treated with 303 after it dries. It is best to kill this stuff before it grows.
In your case, I would recommend what I do with my sea ray. Same mixture on a sunny day. UV light breaks down chlorine and renders it harmless. Soak everything down. Let sit for 10 minutes, wipe it down with a wet rag and clean water bucket and you are good to go.
