Scott-
The plastic and carpet panel is all one piece. Yes, it is only screwed in and clipped at the top just like the door panels, as was described above. Once that's off, you can remove the screws on the metal access panel to get inside the tailgate.
I've been inside mine a couple of times-- once ten years ago running oil through it to keep out rust (must've worked!) and once to look at the plastic guide wheel that's left a wee bit of a mark on the glass over the years.
It's really not that hard. My back window squeals when going up or down, but it's ALWAYS done that. I guess it's just never bothered me.
Good luck!
Kevin