How do I legally dwell in the static house all year round?

Assuming you're in the UK, you need planning permission to live on your own land. I think you can get away with it up to 28 days but for any period after that you'd have to apply to your local council. Their main concerns would be with toilet waste. At a push, depending on how visible the caravan is to nearby housing, you could get away with living there for quite a long time before the council get it together to pay a visit. It only takes one person to complain however.