I like the swing down idea. I've been going back and forth on it in my head because the

likes to drive the truck too. It would be a pain for her to lift a huge freaking tire/mounting arm if she needed in the back when I wasn't around.
Have you thought about adding a strut or spring of some sort to assist with the drop/lift?
Also, instead of a latch for the down position, I was considering a bumper post sticking out to rest on the ground. Then the spare can also work as a step to get in and out of the back.
For the Up position, I haven't got a clue yet. Needs to be STURDY for sure