You have to ring your local office for a quote. Copy this address and paste it into your browser:
http://www.nfumutual.co.uk/you/caravan/caravan-insurance/how-to-buy/
I've just renewed with the caravan club (although you have to be a member). Reason being I moved my caravan and the company I was with refused to continue to cover it because it was on a farm with less than ten caravans total.
p.s. the insurance company you were querying on your other post is *&*, also known by another three similar names.