After reading this thread...
Years ago, Turtle Wax made a fantastic vinyl top wax that went on sticky, but once it dried it was great. No streak, no washing off and for an indoor car stayed around a long time. When it forced off the shelves (contents? who knows...), a clean up man suggested Mop N Glo. It seemed to be exactly the same stuff, went on the same sticky way, did a terrific job. The 1990 Chevrolet still has a coat hanging in there.
After reading this thread, thought I would try to find something. I purchased some of Dr. Borkat's Ragg Vinyl Top Protectant, and a hearse dealer recommended Surf City Garage's Black Max.
I want something to go on and stay on like Turtle Wax or Mop N Glo, both of these have a slight milky appearance and I am cautious about putting anything on yet later, I don't want it to haunt me later by turning white in areas on the top.
I took a piece of vinyl top that was sent by the hearse dealer for the '08, and I have applied each of these products on one side of the vinyl top sample, and plan on leaving in the sun awhile, rain awhile, and wash off with the hose and see what happens.
Will let you know what happens.
(Disclaimer: Do not try this at home. For professional drivers on a controlled course only. Apply once every three days and if a rash develops please consult your medical professional. If legal or other requirements mean you must buy any items you did not specifically ask for, we will explain the reason in writing on the statement we provide describing the funeral goods and services you selected. Should this direction last more than 4 hours please consult a physician)