All one piece.
I put the spoiler on the rolled out vinyl, rolled it around the spoiler, marked up where it lapped over and left another 2" for play. I was a bit sceptical that it would look ok at the join you mention but with heat and my wifes plastic hair removal tool with rubber blade (I kid you not!) it formed nicely into the groove.
Took around 2 hours. The usual 1hr 20 for the first half and 40 minutes for the second once I figured out the technique.
Really worth doing!
Edit - Ohh, and the part where it laps into the light assembly, I left a few mm overlap with the cut and tucked it into the gap with a shell clubcard. Was going to use my credit card but was just that little bit too thick to work with.