factory grounds work, if they do not, you may have tight channels that need to be broke open, stronger welds in places...clean clean clean.
and i found aluminum in the back, with a whiff of air is doing all those straps are doing, all at once.
The trick has been known forever to stubborn cars, today it is called a diffuser and found on ricers most often, with turbo engines.. Down low, in the rear..sometimes looks like a radiator.
I chose a solid sheet of thin aluminum, riveted..in front of rear bumper..nothing to see, it is hidden..blow off the blue crsytals of interaction chemistry once and awhile. Quite noticable on my old subaru. Alot of iron in the old buggy...
