Turns out the tinted windows made the small panel I have only barely able to spin the fans I have if the sun is directly overhead, so I ordered a larger (10w vs 1.5w) panel. Hoping to run 2x 12cm fans, and maybe I'll set the small panel up as a 12v tender. Keeping the car cool when parked should help extend the life of the hybrid battery.
Monocrystalline Silicon Hobby Solar Panel 18V 10W 555mA for Home Lighting | eBay
The cabin air filter is behind the glove box, protected by a bunch of bolts.
Filter really needed to be changed, made a noticeable difference in the airflow through the vents.
Also, was recommended this for adding an integrated voltage monitor to my grid charger:
http://www.ebay.com/itm/DC-DC-Conver...item563e4c581f
Most cheap voltmeters that can be run on 12v are not properly isolated and will thus cause a CEL if you use them.