Hi Rich
We were in exactly the same position as you up until a few months ago. We wanted a people carrier but found that the older models eg 2007 and under what we could afford didn't have a great towing limit.
We ended up with a Peugeout 307SW estate 136 and we absolute love it.
There are three seperate seats in the back, which you can easily fit 3 car seats. The beauty of this model, is that you can also buy 2 additional seats to go in the back thus making it effectively a 7 seater. Some of the models come with the 7 seats, unfortunately ours didn't. It has a towing limit of 1400 kg and we have bought a Sprite Major 6 with an mtplm of 1425kg so we will have to make sure that we don't load it up to its max.
I know they also do a 5 berth in this range, the Sprite Major 5.
If you want any further info the please don't hesitate to ask.
Sam