Larry, even if vinyl tops were required for louvers I wouldn't add one. I'm just trying to arm myself with knowledge for questions I'm sure to get asked.
I hear ya' considering hard tops. Before my last two cars, my two keepers were non vinyl tops. I like 'em that way. One thing about living in the Northwest, if you drive them you're gonna get wet & when that happens the protectant you put on the roof makes a mess.