Hello Dave,
The caravan manufacture is supposed to leave both the user and fitting instructions in the caravan with the appliance. Read them, and if it states the appliance should be sealed and it has not, then the you seller has failed to supply a caravan free from material manufacturing or design defects. This is breach of the Sale of goods act. It is also a breech of Gas Safety Installation and Use regulations that require the fitter to install a gas appliance in accordance with the manufactures instructions.
Despite the non-conformance of the installation, the danger from an incomplete room seal on a caravan fridge is in reality very low, because the size of the flame is relatively small, and the amount of fixed ventilation in a caravan is high. There is greater danger from the open flame on your cooker hob.
Never-the-less the caravan manufacturer's should be installing in full compliance with appliance manufactures instructions.