Measure ( dry fit) 2X 3X, 4x , cut once. I taped it on my truck for fitting every time. I bought a thin rubberized liner with w/adhesive backing from Amazon . I cut it to size the side of the snorkel that touches the truck, all the way to the scoop, to eliminate rubbing and a secure fit.
i used a jigsaw w/ a very fine metal cutter To cut the hole in the panel. They provide you with a template for that.
My only regret, if I can redo mine, was to swap out the hardware that came with it. The screws were short and I had to really struggle to get it in and tighten it. Replacing it with a longer stainless one would make your life easier. And of course, SOP, paint all cut up metals and plug all holes w/ silicone