All of the insurance companies are asking about this now, water tanks etc. It can be expensive if not with a specialist broker, and if you don't tell them about it then it invalidates your insurance. (And don't just tell them on the phone, you need to get it added to the policy wording and sent to you)
Best bet it is to go with a specialist broker. I went with Alexander Swan, I pay £85 a month which covers the van, and the system is covered for replacement with like-for-like replacement and fitting cost (pure2o). And poles are covered.
I had a laugh at direct line's quote, they also wanted to know about water tanks and how they're secured.