Hello Kestrel,
At the risk of repeating what others have said, for over night heating and safety probably a convector type heater may be best. They are quiet, and usually have a built in thermostat so they will modulate the amount of heat they produce to maintain a preset temperature. Care should be taken to prevent any thing from covering them, but in the event usually the thermostat will prevent over heating.
The draw back of convector heaters is that the air inside the caravan will tend to stratify, with the hot air at the roof level and quite cool air a foot level. This can be uncomfortable. I have actually measured the temperature range in a caravan and found air at 5C at the floor and 30C at the roof. (external ambient of -5C)
A fan heater does much better at mixing the air (blown air heating on a caravan heater does better still as it ducts the air) But there is the noise factor of the fan, and the heater is more sensitive to being covered or having its air ways obstructed.
Radiant heaters are good at warming surfaces in direct line of sight of the element. The down side is that surfaces in shadow can be much cooler. The difference between warm and cold surfaces can very noticeable and consequently uncomfortable. The majority of shop bought infra-red heaters use elements that operate in the shorter wave-length visible light range. This makes them quite bright. There are more expensive Quatrz element heaters that use long wave-length IR radiation which are not as bright but produce just as much heat.
Some advertising make out that a particular models of heater are high efficiency, and by inference that others are low efficiency. This is inaccurate and misleading. One of the beauties of electric heating is that by virtue of convection, conduction and radiance you will actually get all the possible heat from the electricity used 100%. Even the power lost in the cables comes out as heat.
It is a characteristic of heating air that warm air can hold more moisture than cold air. It does not dry it out, the same moisture is there but because warm air can hold more it feels drier. As the ejected air from a fan heater is much warmer than its surroundings, it feels particularly dry, but as it cools towards the ambient it will loose it apparent dryness. Radiant heaters do not directly heat the air only the surfaces they shine on. But as the surface is warmed, the air next to it is warmed, so ultimately the same overall effect will be achieved regardless of which type of heater you use.
The choice is yours.
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