On my dash I use SU 2000 thats what it used to be its in a flourescent green bottle its made by turtle wax. My cover is Vinyl its an Access. What is 303? and where do you get it Walmart Auto part store online???
I used 303 on my Truxedo. Works excellent! Check their site to find a retailer local to you (to avoid shipping costs). Warning -- it's more expensive than your $4 vinyl protectant from WalMart, but it's worth it.