There is nothing so miserable in a nomadic home, as being cold, tired and well, miserable.
The principles for keeping a nomadic home warm and cozy are the same as for a bricks and sticks house: Heat source; insulation, ventilation.
Because my idea of a nomadic home precludes the need to be tied to a fixed electricity grid, electrical heat is not an economical proposition. A nomadic home is only nomadic if it can move at will and remain fully functional where ever it is.
This pretty much leaves combustion as the most likely heat source. There are forced air diesel heaters like Eberspacher and Webasto which reportedly produce very good and quick heat. My issue with these heaters is the amount of electricity they need to run. I have also heard that they can be noisy. Because nomadic homes require enough maintenance to keep them mobile as it is, I try to keep everything else as simple, mechanically, as possible.
Cooking stoves can often provide enough heat for very small nomadic homes, especially if a small ceramic flower pot is put upside down over the burners. Also paraffin/kerosene lamps will add heat, if they are used for lighting. Portable gas and paraffin/kerosene heaters are also available. Plenty of ventilation must be provided if flames are not vented outside, to prevent oxygen depletion and carbon monoxide/carbon dioxide poisoning.
My favorite form of heating is with liquid and solid fuel stoves that have external flues. While exhausting directly outside, they also draw fresh air into the home, increasing passive ventilation. You can usually cook with them as well and nothing improves the atmosphere of a nomadic home in cold weather like the smell of a soup or stew simmering on the fire. These type of stoves can often be fitted with a wet back for heating water and/or running radiators too.
With the exception of the forced air heaters, the hot air will sit at the top of the nomadic home, leaving your feet in cold air. To remedy this it is necessary to keep the air moving, to keep it an even temperature. A ceiling fan blowing down will work if it is practical. Otherwise one or more floor to ceiling ducts can be set up, with a computer fan inside them to draw air through. Computer fans are generally quiet and don't use much electricity.
There are various forms of insulating material available (fibre-glass batts, rockwool, foam matting, expandable urethane foams, double glassing etc..). The purpose of using insulation is three fold. It requires less heating in the first place, keeps heat in once it is created and stops condensation from forming, because the warm air won't be coming into contact with cold surfaces inside the nomadic home.
Finally, good ventilation is essential for not only keeping up oxygen levels but also keeping humidity under control. The typical nomadic home is a small space and is therefore unable to dissipate humidity to the extent that a house does. People breathing, cooking and showering create huge amounts of humidity in the nomadic home and this alone can make it feel colder than it actually is.