Interesting idea, I was thinking I'd be beating/pressing that sheet flashing over a wooden form if I got round to making a diffuser. Heh "Vacuum formed for quality fitment" I thought vac forming was the cheapass way of doing stuff....
I found myself wandering Walmart today, I had an hour to kill, they have some good rubbermaid garbage cans in there, $5.47 each, black or beige that have an improved looking profile over that one I was eyeballing in the washroom. Looked like they could be cut for 2 fairings each...
Also went down the camping aisle and the tent pegs jumped out at me, T section plastic, 6 for 2.47 or something like that, saw the ends off them for airtabs/turbulators, would probably be big enough for most personal vehicles, possibly undersized for big RVs, boxy trailers etc. You could probably get up to 3 out of each peg if you wanna take the time cutting and sanding. I'll have to go through my camping pegs, I know I knocked the hook off quite a few last time I went (hard ground) and I probably just threw them back in the bag. Dunno if I'll find more than a couple that are too mashed, scarred and bent to use or not, but it's worth a look before I go buying extras. Also can get 4 T section ones for a buck at the dollar store when they get their summer stock in, so likely to buy them there. Just need a good double sided tape or liquid nails or something to fix them on with.
Walmart got boring, so sauntered over to Home Depot, was hoping to see a nice grille material, all they had in that line was the diamond expanded lath stuff really. They had a louvred fence system that might be interesting for making a grille shutter system
http://flexfence.com/hw.html also thinking about it for the house, would love to be able to control solar gain on a couple of the walls. Found some interesting stuff in the carpet edging rubber strip area, stuff called "dry back" a rubbery moulding for using for bathroom and kitchen skirting boards/baseboards I guess. Looked useable for airdam bottoms. Kind of a bit disappointed in home depot though, was thinking I'd find some more useful stuff in there. Was investigating the plastic mouldings for use as spoiler/deflector strips but they all seemed a bit floppy.