First panel is done.
Chrome wrap, 10mm fluted polycarb (intended for roofing), panel on top. All fixed with VHB tape. I ran a strip of alluminum over the front of the panel just in case. It's screwed to the factory roof rack points (I have 10 mounting points so I can spare a couple).
Top Tip: Flute polycarb is much cheaper in short pieces than in longer lengths. A 2400 long sheet was $120, I bought 3x1200 sheets for $60. It means one join under each panel, not a big deal.
The temperature of my roof is the same under the panel as it is without, so happy with that.
So far I'm seeing approximately 0.2l/100km gain. Less than I expected, but then that's why I ordered two panels. I wanted to run a single panel for a while just in case the second panel wasn't necessary. As we head towards summer, the gain can only increase.
As the panel smooths my ribbed roof for only a tiny frontal area increase, I should have better aero too.