Yeah, Rhode Gear Co-Pilot very good, their Limo seat is even better, as it reclines, which is better for a six-month-old.
If you're in the countryside, a trailer is an option, for weather reasons, as Zazette says.
Otherwise, there are covers you can buy for the Rhode Gear or similar, that cover the child pretty much head to toe (fit around the seat), or you can put them in layers of suit (fleece first, then water/windproof).
One problem with the Rhode Gear (or any other rear seat) is you can't use rear panniers, and a backpack is also a bit of a problem - front panniers may be your only option if you have much to carry.
In a rear seat, at least they're out of the wind, though - front seats are a nightmare for the wind. (I have a much shorter journey and a much larger child on the front, but still, it's a big problem.)