Hi Melanie,
I too have the Comfortz internal liner, and I wouldn’t be without it, its a superb piece of kit. It keeps the cold out and the warmth in, and still allows for ventilation. Not cheap but you get what you pay for.....
The best bit beyond doubt is that its the classic ‘fit and forget’ item. Once in, you can leave it in situ. The roof will fold down happily with it in place, which for me made it the deal-breaker. When I fitted it on a very hot day, the temperature noticeably became cooler in the roof area, which was very welcome. And similarly, when camping in the cold, the temperature up top stays warm as the liner retains the heat.
So apart from anything, this really means you can camp all year round, with the pop top up, and have an even, comfortable temperature throughout the van.
Oh, and its a very pale grey (almost white) in colour, so makes the van much brighter on the inside, but also keeps the daylight out, so you don’t feel like you’re sleeping in a tent when sleeping upstairs, in other words, no 4am sunlight waking you up!
All in all, it's without doubt the best accessory I've bought for the van, I’d almost go as far as saying its almost essential!