Finally gotten around to a vertical skirt. Some of the self-imposed challenges were 1.) creating a means by which this could be removed without any tools, 2.) creating a stiff and robust installation 3.) minimizing the need to physically work underneath the car to attach 4.) minimizing bracketry that had to be added through the addition of new holes (I wanted to avoid drilling under the car). So by and large I succeeded, though I'm still not 100% satisfied.
I achieved most of my goals by utilizing the underfloor cladding already underneath the car. The Dart is pretty well cladded mid-wheelbase. Thus I was able to remove the underfloor and did most of the work on a bench in my garage (achieving # 3). I did have to add a bracket that mounts to the floor of the car independant of the underfloor cladding, and it's secured at the moment by a rivet. Furthermore, this bracket draws the cladding up as it was sagging under the weight of the skirt (the cladding that requires the bracket is a part I created a few years ago that is detailed earlier in this thread; by its nature it is thin and light weight, thus not particularly stiff across the distance it spans as it never was intended for the task I've repurposed it for). Thus, if the bracket fails, rivet pulls out, whatever, the entire skit will drawdown lower; not catastrophically low, but it would need to be addressed then and there in the event of any sort of failure.
At the leading edge I drew the skirt inboards to achieve two goals. First, I wanted to creat something I didn't have to remove every time I took the car to the dealer for work (oil change, tire rotations, etc.). And the skirt as originally devised would have been only offset an inch or so from where I believe they typically lift the car from. Secondly, I thought it might be worth moving it inboard to further grab the junky air coming off the inboard edge of the front tire. It creates a very subtle 'S' curve in plan. Secondly, the skit is only about 2/3s of the wheelbase. As you go rearwards, the car's floor goes up in X (height), and the surface isn't particularly geometric, thus I would have had to made a deep bracket that mounted to a organic surface shape. So I've punted on that for now.
I've only done the LH side for now; ran out of time (company coming over for the Auburn game at 3:30, War Eagle!) and will tackle the RH side tomorrow.