I think the one of these I owned as a kid is still
in a box in the garage loft somewhere. It was a completely bullet-proof
and indestructible toy. Mine ended up being repainted with fluorescent
paint as a site office on my electric train layout. You couldn't nick
the tyres for a more interesting car that was in need and there was
nothing, absolutely nothing to break.
The coupling is a piece of genius too, the problem with die-cast towing vehicles and trailers is always the fragility of hooks and tow bars. A hook on the caravan that pushes upwards on a cantilever into a half-moon shaped orifice under the rear of the car is simple and almost unbreakable. You'll find most Corgis up to about 1960 had the hole to fit this caravan. The caravan itself is pleasing. A nice thirties-style teardrop shape with flowing streamlined lines, very pretty.
This caravan was produced from 1956 to 1964 and is either cream over blue or cream over orange, both options seem to be valued at the same fairly modest rate