Landlord Buildings and Contents insurance

Hi I have a small portfolio and currently have an individual policy for each of my properties. Does anyone use an insurance company that would cover multiple houses with just one policy. If so does it make it more cost effective?

Also I recently tried to claim with one company who refused to pay out as they said it was damage that occurred over time - it was rising damp that was not seen until tenant moved wall unit. Anyone come across similar problem or did insurance company pay out.