How do I replace insulation of water tank?

We've just had a good ten days away in our 14 year old Symbol. Impeller pump for toilet flush had to be freed up (good advice on this forum) and I've just pushed on a new gear lever knob £11.99 from China via eBay after the original came 'came off in my hand'. 
I thought we had a leak from the underneath water storage tank when there was a large puddle under the van when the ground finally dried out. However the meter didn't show any dropping and I think it was water coming from sodden and tattered insulation as it has now dried out. 
Has anyone got any advice on how to replace/cover the insulation? An attempt to use duck tape resulted in untidy bits hanging down! 

I've had a bit of a search and can't find anything on this elsewhere.

Just remove the insulation altogether, it serves little purpose, it may delay the freezing of the water but equally it delays the defrosting once it happens unless you also have tank heaters.

Definitely don't have tank heaters in this van, although it has all the essentials. Thanks for reassurance about removing the insulation. It will be easier than trying to replace it.

Totally agree with Crosgor

Perhaps only insulate the pipes? They will freeze first. Easier to do and stays on. I'm about to do this, having removed the tanks to replace the leaking taps.
I fitted foil-backed foam insulation whilst the tanks were under the van. Some of it fell off. When the tank overflows, water gets underneath the insulation, making things worse. So I stripped it off.
In the winter, I'll take a few 5 litre water tanks and fill them regularly.

Absolutely spot on!

Excellent advice from both respondents. 

The tanks on my van do seem very low and found that the underside insulation (silver sided bubble wrap) had ripped so I decided to replace not like for like but fitted a sheet of 3mm marine plywood, the insulation property is on a par and it also gives protection to the tanks.