So I just got off the phone getting my new insurance with Octagon, and am so happy as I saved a 1000 pounds next year. I just thought i would share my experince, because what happened was, the lady on the phone told me straight away they couldn't insure me with the water tannk. I read old posts about this issue, and basically said this: Thanks windyman. I asked for the manager, she said she would put him through, after 2 minutes same lady tells me 'yes we can insure your van, as your water tank isn't classified as modification. Well happy with my monthly installments!