The top wood is predrilled in every hole (230). Every other hole is used to hold the fabric down and the alternate holes for the base. I used #4 1/2" stainless flat head for both applications. Pick up 20 3/4" as you may need a few. #19-1/2" wire nails across the front will be buried in the fabric under the aluminum base.
My start is in the middle of the rear. be sure to leave a long enough back leg to trim to fit.
The aluminum base is about 7/16" wide and covers almost all of the silicon fillet.
As you tighten the silicon fillet will level out and variations in the base can be controlled with tightening.
I purchased a package of thin cutting sheets in Wal Mart for about six bucks. These are absolutely wonderfull in the kitchen and the only way to go when trying to protect stuff on this job while using cutters or saws. Slide'em under the base and you can prevent damage to the car.