I thnk both wee covered in article in CC magazine a couple of issues ago. CTEK got a very good write up - you can download the leaflet from the Roadpro site. They are fairly expensive, but appear to be suitable for charging both leisure and car batteries and to be able to charge the car battery without disconnection. This is not recommended with other chargers as the fairly rough DC can damage the electronics. Mercedes offer CTEK as an accessory (but at MB prices) so presumably they think it's OK.
The larger of the chargers will also provide a useful Dc output which would supply the caravan in the event of failure of the fitted unit, so you could consider it a useful spare as well as a charger.
(Put CTEK into Google for other options)
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