We have a minivan with captain chairs in the second row, and we have both boys in those seats. We really only use the 3rd row (for people) if family is in town visiting. In that case, they can get in pretty easily before we snap our younger DS' carseat in the base. We actually fold our 3rd row seats down more often than use them for people, so having them both in the 2nd row was just the obvious choice for us. Plus I can see them both in the mirrors better.
Re: RP link: Where to put carseat in minivan