A little late, but I haven't checked in here since my 2nd daughter came into the world 13 months ago.
Good call on the Megacab. The quad cab is just a poor design all together. The engineers and developers didn't have families in mind when they designed it that's is for sure. A rear facing car seat will fit, but like previously stated, the passenger will be hugging the dash, as a rear facing seat behind the driver isn't possible, at least not possible for me. I'm in the process of trying to sell mine now for that reason . Going to pull the trigger on a 2016 crew cab longbed. Automatic this time, so my wife ca drive it.