So, this evening, I made a small undertray that just covers the underside of my front bumper, and panels to A) sort of ghetto-fix my hacked up fender liners, and B) provide little blocks in front of the front tires.
Mocked up on the kitchen floor:
It's tough to see, but that's the undertray fit in place:
Is there an actual name for what look like mudflaps in front of the tires?
I reinforced them in the engine compartment with disassembled wire hangers.
...and a detail shot:
I'm going to see how it all holds up driving to work the next two days, before my trip. It will all likely need some reinforcement, but my drill is charging, so that will have to wait a bit. If there are gains to be had, they'll show at least a bit on my commute, too, since most of it is at 40-50mph.
I found an interesting way to mount coroplast, too: christmas trees! More formally known as panel clips, they are cheap, and easy to work with. If you can't get your hands behind a panel to attach a nut to a bolt, you can probably jam a christmas tree in there, if it's not a load-bearing piece.