... do I really need this .
I have paid them a lot over the years and wondering is value for money just knowing if anything happened im covered enough . Your thoughts much appreciated.
There is no legal requirement for you to take out cover for your caravan. As others have said when its coupled to the tow vehicle and on the public roads, your standard car insurance also covers trailers under its third party cover.
But that does mean you are not covered for losses to the caravan or its contents when on the road or when its uncoupled. That is where the cover you have been using from the "CMC" fills in the gaps. And adds third party cover for when you are on site or uncoupled.
Without the CMC cover , you could be held personably liable for any injury or loss involving your caravan when uncoupled anywhere including on site or in storage.
Some storage facilities actually make having third party caravan cover a prerequisite for using the site.
The choice of risk is yours.