What's the difference between KVA and watts?
Watts = KVA x 0.8. Therefore a 5KVA generator only produces 4000W and a 5000W generator is 6.25KVA.

I think it's something to do with load factors, ie. the ratio of resistive to inductive loads but this is getting a little technical for me.

What type of generator should I buy?
A quite one! I know the tradesman-style gensets are a lot cheaper than those designed for motor homes but they are very noisy.

If you've been to a rally or campsite with them running you will appreciate that noisy generators do more then generate electricity, they also generate extremely high levels of ill feeling in your neighbours.

This was driven home to me at the Roma rally; because the weather was overcast many of the big rig's solar systems couldn't match the demand so it became necessary to fire up the gensets. Often the owners then headed for quieter pastures and left their neighbours with the noise. It was BLOODY annoying.

A properly installed Onan (there may be other brands as good but Onan is the de-facto standard) genset will be almost impossible to hear, but be prepared to spend two or three times as much as a cheap Honda.

How do I calculate the power used by a device?
Watts (power) are calculated by multiplying volts by amps. ie. if a 12V device uses 2A then it consumes 24W.

How do I get 12V from 24V?
With a regulator. There are two main types, switch mode and resistive.
Switch mode regulators are usually more expensive but the are a lot more efficient. They convert the voltage by using high frequency switching. This process can cause a lot of RFI (Radio Frequency Interference) which I have known to cause problems with CBs etc.
Resistive regulators simply divide the voltage to provide the 12V. The difference is dissipated as heat. This is very inefficient but also very reliable and produces no RFI.

If I have a 24V battery bank, can I tap 12V from one of the batteries?
Yes but it's generally frowned upon because the battery being tapped will discharge differently to it's peers. For very small loads it's OK but try rotating the tap to other batteries periodically. For large loads consider a regulator or separate bank.

Why use 24V instead of 12V?
Mostly to reduce wire size. In large systems the currents can reach several hundred amps. By doubling the voltage you halve the current and this allows you to use smaller wires.
Many trucks use 24V for the vehicle electrics. In this case it may be easier to also have a 24V battery bank because you can use the engine's alternator to charge the house batteries while driving.

Should I have a separate battery bank for the house?
MOST DEFINITELY. Using the car battery for the house is just asking for a flat battery. Very inconvenient if you're bush camping.

What's the relationship between Amps, Volts, Watts?
W = A x V
V = W / A
A = W / V

Are 12/24V devices more efficient that 240V devices?
Intrinsically I don't think so. But 240V appliances require the voltage to be converted from 12/24 to 240. This process is usually about 90% efficient so there's a 10% loss there.

However it seems that fridges are different, a standard household fridge will use 2-3 times the power of it's 12v equivalent.

Should I use gas or electric heating?
Both. Gas is a more efficient form of storing energy than batteries so when you're bush camping it makes sense to use gas for a high-energy requirement like this. Especially when you consider that the reason you need a heater in the first place is probably that you are camping in an area/season that is sunlight challenged.

However, if you're paying extra in a caravan park because you are hooked up to electricity then you might as well use as much as possible. Check the legislation regarding unflued gas heaters before you commit to one though.

Should I go for a gas or electric fridge?
At every rally I go to the campfire discussion eventually gets around to the subject of keeping gas fridges cold. People have all sorts of tricks involving thermometers and things for levelling vans. Not once, have I heard of and electric fridge owner having to do anything more that turn the thing on. This tells me that electric is the way to go.

However electric fridges use a lot of power and a small rig that would not have a large enough solar system for an electric fridge could easily carry enough gas to power a three-way fridge. So I guess the answer is, for small rigs, use gas/three way fridges; for large rigs, use electric.