I havent used the solutions mention above by Steve, but I do know they work very well for irregular surfaces, it's on my "must try someday" list. If you watch the youtube videos on it its pretty impressive stuff.
Putting the decal on shouldnt be a problem if its curved in just one direction, curve in both directions makes it much harder, not sure if the taper you mentioned is a compounding curve. I've done slightly concave areas and its not easy, I had to work it a long time. I commonly hear use windex, but the windex disolves the adhesive, a very mildly soap-water solution (like just a few percent soap) is better from what I hear.
I would use a lot of solution and work it middle to out with a squeegee. Dont get the decal liner wet by accident, I've done that before, it sucks.
Last edited by Paul Bell; Mon Jun 01 2020 11:09 PM.