Winterise a caravan and drain down

Many static caravan parks are located by the sea, which only adds to the problem of over wintering because of the damp which may promote mould growth. One tip to beat the damp in the air is to use washing up bowls full of cooking salt. Usually one at each end of the caravan is sufficient, but you may also play safe by adding small plastic bowls spread around the rooms.
When you return to re-open the caravan, the salt will have extracted lots of water from the air into the salt bowl.

Furnishings and cupboards. If possible remove interior cushions & curtains and store at home somewhere dry.  If you are unable to do that, then prop up seat cushions and pull away from sidewalls to allow free-flow of air. Also leave all the caravan doors open to allow air flow. As there are no curtains to keep out the light, make sure all furnishing are covered with a thin bed sheet to avoid fading in sunlight. But even better than this, you could purchase some of those vacuum storage bags and use your hoover to suck the air out.  Remove all tins as they will leave a rusty ring on the shelf. Clean and empty refrigerator and leave the door open a few inches for ventilation. Clean and de-grease the hob and oven.
Rodent Proofing One common problem which is possibly the biggest nuisance after a burst pipe is mice. Rodents like to find somewhere warm for the winter and will easily get through a whole the size of a wedding ring. So make sure you have a wire mess screwed over any hole or air vent i.e. in the boiler cupboard, under furniture, under the sink, fridge etc. Always make sure you remove all food items.
Mains water (taps) You may need to contact a competent person for this job or ask the park maintenance. But it's not difficult to do it yourself if you are usually good at DIY. Turn off mains water, disconnect at the joint and remove the handle (just in case someone tries to turn it back on). Open all the caravan drain taps under the caravan, then run off any water / close again. Open the taps in the sinks/showers etc and blow through the mains feed so the water is expelled into the sinks. This is because there are 'non return' valves if you try to do it in the reverse direction, and will leave water in the pipes. Leave all taps open. Flush toilets inside to empty the cistern.  Place a small amount of de-icer in the toilet bowl, cistern and all sink plug holes.
Central Heating & Boiler It's important that the boiler is left operating as normal during the winter for 2 reasons;  1. So the caravan keeps aired and dry  2. So the boiler does not seize during a prolonged period. To make sure sure the system does not freeze (especially the mini bore pipes in the boiler) you need to check the antifreeze levels in the system. There is a special tool for checking this but it's only available to tradesmen at approx £100 each. If the system is low, its best to top up to -15 degrees centigrade with a Polypropylene Glycol antifreeze. This is the one suggested by many boiler manufacturers and insurance companies, but it is also more expensive. Boiler manufacturers do not recommend using automotive antifreeze in a boiler. In addition, automotive antifreeze is highly toxic and may encourage pitting inside the boiler, leading to leakage.  Possibly the best known brand of antifreeze is Centinal X500 and you can either; 1. Pump it into the system via the inlet fill 2. Isolate one radiator, drain off 5 litres of water and refill through the top plug with radiator funnel.  Leave the radiator on a timer to switch ON for 15 minutes once EVERY HOUR and leave your radiators on the frost setting. This means you are protected again a hard freeze and the pipes will keep warmed every hour to prevent and damage. Also if there is a power failure, the clock setting are always going to be correct (i.e. ON once every hour) You will not have a huge gas bill by doing this because the boiler will only fire up every hour just enough to warm the pipes to protect them. This might only be for 1 minute, or not at all if its not below zero degrees centigrade.

Other tips
Remove any clock or smoke alarm batteries that might corrode over the winter. Fit new batteries in the spring. 
Gas cylinders should be removed and stored in a cool, well ventilated location, preferably not in the caravan.