Based on information posted here previously, I liked the idea of using the supplied mount to put the camera into the back window. In my RV, putting it on the upper cross-member would make it too high, and I couldn't mount it to the bottom, as shown in those pictures, because half of that window slides open (to the right) and is, in fact, the "emergency exit".
What I came up with was to use a foam-rubber block that would sit in the frame of the window (at the bottom) but could be easily removed. I found this at Hobby Lobby:
(No, I didn't buy it because it was "pretty"; the one with this design gave me the largest block of rubber to play with.)
I cut a piece the width of the block and 7/8" down. This slides tightly into the window frame (but can be removed). This foam is dense enough that I can just use the supplied screws directly into that foam. Here's what it looks like pressed into the window:
Here's the block by itself. Note that I left the pink stuff on the bottom just to give it added depth:
I can tell even without trying it that the camera is too loose on the bracket they supply and it's going to shake like crazy. I may try taping the camera to the bracket, but in the end, I think I'm going to need to put a piece of soft foam between the camera antenna and the window and just tape that antenna to the window itself. I'll know more in a few days.