1. Dear *****sy, I regret to say that you will need planning permission to site a static caravan on the woodland. This is because a static caravan is no longer a temporary structure, so as a result, it requires planning permission. It would only be a temporary caravan with wheels which would not require planning permission. However, once you take the wheels off and attach things such as water and electricity, you require planning permission.
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3. Essentially, so long as your caravan can be removed immediately, for example, if it is on wheels and can be driven away, it is a temporary structure. It is only if the caravan rests in a permanent form on the ground that it needs planning permission. The example, I gave of taking the wheels off is making it permanent. Adding electricity making it permanent would involve a connection to the electricity supply. Obviously, if you are using solely solar panels, then this is not a connection to the main electricity supply and so is temporary. Again adding water would involve connecting to the water mains and making the connection permanent. These are examples of making a structure permanent so it needs planning permission.
4. There are exemptions in the planning code for sheds. However, once you live in the shed it is a residential structure and you would need planning permission. Planning permission is required for all residential structures which are not of a temporary nature. Normally temporary is interpreted as meaning six months.