We have the onboard tank on our caravan and it has the surge damper fitted as the system also has the onboard pump. There must be a good reaosn for fitting it otherwise to save a penny manufacturers would not be fitting the unit.
The decision on whether to fit a damper of not will depend on
a. How much they want to charge for the caravan
b. On the other pieces of gear in the system and how they are connected up
If the caravan manufacture fits the standard Watermaster pubinary On/Off pressure switch with similar characteristics to the the original Whale pressure switch. This can give rise to pulses of hot and warm water I described earlier.
The Watermaster IC unit works differently. apparently it somehow monitors both the flow and pressure, and adjusts the power fed to the pump to match the demand, but crusishally keeps the pump running, so both hot and cold systems maintain an equalised pressure preventing the alternating pulses.