I too have a recaro sitting in the middle of the back of our '03. Works great and easy to take in and out. Since I'm in a job where I often have people in my car I routinely pop the seat out and set it in the trunk area. Also great to be sitting while screwing with straps. As the little guy's gotten older and opinionated it can be a lengthy process

And nice too when it's raining or snowing. By contrast my wife's 330 has it on the passenger side so I about kill my back leaning in from outside screwing with it.
We have our 2nd on the way so bought an M5 to replace the 330 since it's too small for two rear facing seats. Will have to play around a bit with placement in both the X and M to figure out the best config for two seats. Regardless, the days of sitting inside while buckling appear to be over for me.