Nothing to add here that hasn't been said. I had an arctic white corvette. P21s is a great wax for it's price but on white a sealant is the way to go. Do yourself a favor and pick up an $11 bottle of Duragloss 111 or a tin of FK1000P.
For me, clay has never ended up as filthy since that initial decon when my car was brand new. And mine was prepped btw. I followed it with an AIO then a pure sealant. It went from white to blinding.