If you suspect your damper is not wroking correctly, try the advice already posted.
Also check the temperature of the brake drums on the caravan after a short tow - they should be only just warm (touch carefully).
If the damper has failed, it is likely that the van brakes will have been applied more than normal and thus the drums hot.
I've just had a similar failure - diagnosed after finding I needed to use engine power when towing down a long hill, and also that after a very slow and gentle stop the coupling was completely compressed,
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If out of warranty expect to pay