I will be using a heater for the freezing nights, but just wanted to make the insulation of the van more efficient.
Also I have noticed a lot of condensation on the roof, so thought this could be solved with the product,
Thanks for the replies 
As far as the condensation is concerned, you must make sure that you keep your van dry. The main problem comes from the hose reel when you have finished with it. We have got some silcone adhesive and filled a couple of Hozelok connects with it, squeezed it in when it had formed a skin on the outside and left it to set for a few days. Our hose reel is outside the van, so when we disconnect the hose, we let it drip whilst we empty the hose from the van port to the hose reel and then push this doctored Hozelok on. This stops the water dripping into the van.
Brushes are shaken off before they are put inside, and anything wet is stored in a plastic box and dealt with at the end of the day. When I get home I will also let the van air with the back doors open for an hour or so when the weather is dry.
I saw a van the other day that looked like a tropical rain forest inside, very unpleasant when everything you touch is wet.