No idea what stains are from but try wd-40 for cleaning
I used spray 9 marine on my whole boat after a buddy told me about it and also used those white magic erasors on the really bad spots and what a change. I also used the erasors on my trailer awning and came out just like new
well now that you're done yours feel free to come up and do mine for me
There was a Dollar store here were I'm at{ in Canada} that sold the Totally Awesome brand cleaner but the Dollar Store shut down.Most of that looks reddish which is mold. It is very difficult to remove and takes a lot of effort. The best product for cleaning vinyl is called Maco but it is very difficult to find. 303 and Babes work pretty good too as does a cleaner called Totally Awesome that you buy is US dollar stores. No matter what, it's going to take a lot of work to get that clean. Once you get it as clean as possible, leave it in the sun. The UV helps break down the mold.