I am afraid it will have to be serviced to maintain the guarantee. If it has not been serviced there is a small chance that something has deteriorated over that period and the service should pick that up. The main reason though is to make sure there is no damp, a damp check is vital. If damp does develop then this needs to be caught in the early stages as the damage can only get worse if left.
Some items are covered by the makers of these but they often have the same one year requirement.
I hope the caravan has not been left stood on the same spot with out moving at all, as if so flat spots can develop where the tyres are in contact with the ground. Even if you only move a quarter of a turn of the wheel it should protect you from this problem. I would do this every month if possible but certainly not less than every three months.