Hello Barry,
When using a 12 to 230V inverter, it is better to have long 230Vac mains side lead rather than long 12V dc leads.
The power losses at 230V due to cable resistances are much lower than losses you would get on the 12V wires. So Brum is right to keep the 12V wires a s short as possible by mounting the inverter as close as possible to the battery, and to extend the 230V side to reach a distant point in the caravan.