i think the insurance price will depend on the size of the water tank,maybe because of the weight.
i have a 400ltr baffled tank for car valeting, i wasnt asked about it when getting my insurance setup. when it came to getting my bro in law set up he was getting outrageous quotes for insurance but he told insurers he had a 4000 litre tank by mistake which is a bit too much for a vivaro van lol. his cheapest quote was £7k .
my insurance is £660 on a toyota hi ace , but im only just 25 and no previous ncb and a speeding fine lol.
lew