I looked at the ebay example, this 'MAC' was once state of the art and fitted in 'high end' vans, sadly though a long way from it now!!
There are two others found by a search for 'caravan battery chargers' one was a long defunct companies 'HM4' from a mid 80's ABI and of little output on a good day, the other a 'LOGIC1' which is simply rubbish and IMO a fire hazard!.
So overall ebay may not be the place to buy a charger for your van, at least at the moment!?
I'd go with a new one, with at least a 12 amp output, many are more than this but 12A should be enough. Plug in Systems, Sargent are two or you could replace it with another Zig although there are plenty of other modern choices