Today I did a bunch of prep and reconnaissance under the car.
It was pretty cold - with wind chill, it felt like 35º F. Progress should pick up when the weather gets warmer, hopefully soon!
I measured the positions of the added fastener positions in the aluminum front panel, and marked them on the underside of the panel. So when it's back in I'll be able to measure out the locations for the holes in the first coroplast sheet. And I reinstalled it. All the well nuts are in, held in place with screws and washers. The coroplast panel isn't ready yet.
I got both oem plastic aero/protective side panels off, and removed the fasteners along the rocker panel bottoms. So the new panels can get tucked under the rocker panels' inner lips.
Those fasteners like to break on removal; they're old. I maybe can get similar replacements. Or since their holes are 10 mm diameter, (rocker panel mount holes) I can use well nuts made for #10 screws, similar to the #8 well nuts I used in the fastening points I added to the aluminum belly pan.
As Ecky and Natalya did, I'm planning on spanning the sheets across the car. The joints between pieces will run crosswise. I plan to fish scale the joints - overlapping in the direction so the air can flow over it. I'm not going to try for butt joints.
I also made measurements for the first (forward) coroplast panel.
It needs to be 46" wide by 24" front-to-rear. That will reach from the row of mount points I added to Scott's belly pan, going back to the first four mount points originally used for the oem panels. Those are M6 screws, with 10 mm heads. It won't cover the full width of the car at the firewall but that's OK.
I have 3 coroplast sheets, 48" x 96".
I will cut one down to 48 x 70.
That leaves a piece 48 x 26.
That will be my front piece, that needed to be 46" x 24". A couple extra inches will be fine. I doubt it will matter which direction the coroplast channels run.
As for the remaining piece - 48 x 70:
In the area between the firewall and the rear bumper, the maximum width I found that I'll need is 68". That's at the firewall, it tapers narrower as it goes back. So the 70" wide piece I'll make is planned to be able to span that width.