Our fresh water tank is inside the MH (under a bed) so has no additional insulation, however both the grey and black waste tanks are under-slung and have heated pads in addition to an external insulated layer. I wonder if you would consider heated pads such as these for your fresh water tank. They are low wattage as they're only intended to keep the water from freezing. Basically though, any insulation layer that does not act like a sponge should suffice to minimise the risk of the contents freezing, and of course a full tank will contain more "heat" than an almost empty one, so minimising the probability of freezing. Gordon.

hi ,,will do ,,anyone recommend how to insulate the water tank i was looking at using it over winter if possible ? just the fresh water as i can use the waste hog if its cold ? 

Hi Rob, let us know how you get on with it, nothing like personal recommendation

just bought one tried it on a similar motorhome and it looks and fits perfect only time will tell if any good i bought it from todds motorhomes,, they seem pretty good ,dont think they would be selling if the were rubbish