First of all make sure that no foodstuffs are left inside the caravan which could attract mice.
Stand seating cushions away from the walls of the caravan to reduce the chances of upholstery damage through condensation.
Open the water system drain tap to drain the boiler, open all taps including the shower and remove the shower head and pipe.
Run the water pump to expell as much water as possible from the system.
If a water filter is fitted remove it.
Empty the toilet completely including the flush tank.
When all water is expelled fit the sink plugs into the plugholes, you might want to use disinfectant to clean the waste pipes first.
Ensure that the gas bottle is disconnected, fit your wheelclamps.
If your caravan alarm is to be left on ensure that the battery is fully charged, otherwise remove the battery for home storage and trickle charging over winter.