Here's part of a post I put up when I installed the flaps on my 2017, I assume they're unchanged for 2018. The jack nuts are easy to deal with if you do the following.
When you read the instructions the first thing you'll probably wonder about is the need for a tool called a jack nut tool. You don't need it, a bit of easy improv will work fine. The jack nut tool is sort of like a large pop riveter, designed to mount a jack nut (a sort of metal expandable fastener) from one side of a panel. Since you attach the jack nut to the lower over fender piece after you remove it you can get at both sides of the jack nut. So all you need to do is get an M5 bolt about an inch long, screw it into the nut from the rear, than put a couple of washers and a nut on the other end and torque it down so that it expands into its locked down state. This will make more sense if you have it in front of you, but it took no time at all to get it in place.
I would add that you need to pay attention to the jacknut's orientation when you put it in, if you do it backwards you're pretty much S.O.L. since the jacknuts are a one shot deal.
Hope this helps...