If your charger came with an O-ring set as well as clamps, I would just wire it to the battery. 10 minutes tops with a cordless drill.
1) Open trunk
2) Peel back carpet(if equipped)
3) Remove absurdly long torx bolts
4) Lift battery cover
5) Remove nut on positive terminal
6) Install red O-ring on stud
7) Reinstall nut
8) Remove nut on negative terminal
9) Install black O-ring on stud
10) Reinstall nut
11) Complete steps 1 thru 4 in reverse
When the pigtail kit is installed, whenever the car is parked, all you have to do is reach inside the rear diffuser, pull the connector out and attach.
This way, there are no cords laying on the paint of the front bumper or fenders.
I know the steps laid out are comically simple. But that's the point. It really is that simple. Even a caveman could do it.