Good aerodynamic articles
 

Tuft testing: https://www.autospeed.com/A_111110/hD...s/article.html

Using a pressure gauge for aerodynamic measurement: https://www.autospeed.com/A_111111/hD...s/article.html

Undertrays, vents, spoilers, etc (3-part series):
https://www.autospeed.com.au/cms/A_2159/article.html
https://www.autospeed.com.au/cms/A_2160/article.html
https://www.autospeed.com.au/cms/A_2162/article.html

These are all about speed/high-performance but would adapt easily to what we do.

It definitely makes me want to do some tuft testing...not only does seeing it remind me of how cool it is, but that last link has data directly contradicting what I've learned here about the area at the base of the windshield, which would put wiper parking position back into play as a possible improvement.

DIY rear undertray howto, didn't help on the tested Insight:
https://www.autospeed.co.nz/cms/A_110872/article.html

Edit: More on measuring aerodynamics: https://www.autospeed.co.nz/cms/A_109741/article.html