I've now built a plywood trunk rack, and it's in primer, with bolt holes drilled (but not yet countersunk) to bolt it down where the silly little hook for the bottom of the portable charger bag had been bolted.
trunk rack in primer by James Lampert, on Flickr
The portable charger bag will go on the left side of the partition, and the donut (EZ Spare or otherwise) will hang on the right side.
Monday evening: countersunk the bolt-holes (having picked up some black-finished 6mm flathead Allen screws at McFadden-Dale on my lunch break), and then spot-primed them, and then shot a thin second coat of primer on the underside, to seal the dust from sanding the first coat.
Applied the first finish coat after dinner.
Also applied touch-up paint (now that I have some) to the hole I'd drilled for my "Flap Ajar" indicator wire. With 2 coats of cold-galv and a coat of touch-up paint, that hole is an extremely tight fit on my homemade grommet. Also put a coat of touch-up paint on the Gorilla Tape holding the wire as it passes through the door jamb.
The trunk rack now has its second finish coat. Still looks like painted plywood, but it looks much better now. Third coat Friday evening. Another picture when it's installed (probably not until Sunday afternoon). No actual hanger for the spare until I have a spare to hang on it, though, since that will have to be designed around the spare itself, with both the spare and the rack actually in the trunk.