It just might not be logistically possible to have the RFing newborn in the middle. If you can't get them in and out without breaking your back, it just might not work. If you've got a capsule and you can harness up then lift the capsule in after, maybe, but they get heavy too! So I'd go baby behind passenger seat if not in the middle. Child lock the door on the drivers side if you're worried about escapees onto the road. But it will be about how the seats are going to install correctly too, there may only be one or two good configurations to even get the seats installed that will decide for you in the end.
I just always try to have them with the most vulnerable, being the youngest in the safest spot possible in case of an accident. So if the middle is out, then passenger side is next safest with the drivers side last.

Good luck You might just have to try installing and see how you go.