I'm working on replacing the door speakers and found there's also a large cavity underneath the door pull. Looks like enough room to mount a sizeable crossover. I think the speaker mount is plastic with room to force a 6.5" with some work - I purchased the Infinity Kappa 680.7cs which has 6x8's barely larger than OEM, as well as crossovers the size of a small paperback. I'll post a pic later this week once it's done.
Who needs tools? I pulled off the door panel with my fingers - in the dark! Oops, missed a couple of little white plastic grommets, will have to go after them in the daytime with a pair of pliers.