dash cams

Hi guys and girls, 
After been cut up again at a roundabout this weekend, whilst towing the caravan, and idiot drivers trying to pass in places which aren't appropriate, and causing us to stop or swerve to avoid an accident, which isn't always easy when towing, we have decided to purchase a dash cam.

As there are so many out there on the market, it looks like a mine field to me, so I was wondering what other folk use and what you would recommend, Ideally I would like it to record and store for a couple of days, till we get chance to save/download anything we need when we get back for our trip.

Thanks in advance.