Thermal 3 rating
It occurs to me that many caravan manufacturers quote that there models have Thermal Insulation Grade 3, saying it can be used all year round with no problem.
But the criteria to meet the thermal 3 rating is... the interior warms up from minus 15°C to 20°C in under 4 hours and the water system still works.
No to me that just means the heater works really well, or has a high enough output to keep the cold at bay. I am sure a tent could pass this thermal 3 test with a powerful enough heater inside it.
Shouldn't a test for how good the insulation is be with the heater turned off, and monitor how long it takes to drop from 20 degrees to 15 degrees when it is minus 15 degrees outside?
I think this would be a much better indication of how good the insulation of the caravan is, and would be a better indication of how much electricity or gas is required to keep you warm in the winter months.
Nigel