Neal, I have found Mardon very reasonable and flexible. I know it doesn't help, but if you had discussed with them the situation before the event, they may well have amended your policy to suit. I did contact them before purchasing my wheel clamp and asked if it needed to be Sold Secure rated, but they advised it didn't. I have also fitted a Data Tag kit which has RF id's all over the place and stickers and marker fluid for electronics (and the registration number on the bow - as per on all JetSkis).
They have amended my policy to cover my boat being on the water overnight when I take her on holiday. The "standard \ normal" policy wouldnt cover it, but after discussion their MD advised they would at no extra charge and amended my documents. I can't ever see that happening with car insurance companies!
I guess the devil is in the detail, much like, many home insurance policies state that you need to have 5 lever mortice lock that conforms to BS3621!