I'd go with the butyl tape, although I wonder how that would hold up under all environmental conditions. Up here in the Pacific NW we sort of get it all. I can tell you from experience though that the RVT only works so well. Eventually the cowl warps again. Here is my play: next time either of my LR3s need a new windshield, I'm going to also get a new cowl. When I do, I'll try out the butyl tape.

 

Butyl tape works great for decades in rv usage in my experience.