Neither the magazine review not the Elddis spec sheet give information about the insulation. You could try asking Elddis directly.
A fully winterised motorhome would have sufficient insulation and heating to cope with contantly sub-zero day and night temperatures, all plumbing should be inside as should fresh water and preferably waste water tanks. I think it would be difficult to fully winterise a motorhome that was not built that way to start with. I also think that you would be hard pushed to find a UK built motorhome that was fully winterised.