The pictures you have shown us of your caravan only shows an ABB DS951-A protection device. This is a Ground Fault detector for the mains 230V ac supply and suggests the caravan is not built/converted to a full UK standard.
Many continental caravans do not have an onboard battery system, and rely just on the mains power, in which case the Sargent switch panel you has suggested you want would not be suitable as it is designed for 12V systems only and not mains power.
It is possible to put in a 12V system, but the Mains wiring should also be brought into line with UK standards, and the fact you have had to ask does suggest you don't fully understand the wiring in your caravan. I suggest you contact an Approved Workshop Scheme engineer to view the caravan and advise with the benefit of being able to view the situation first hand.
Remember that even 12Vdc electrical fitting if done incorrectly is still dangerous.