Never done Christmas day in the van but i have been away over the Chrismtas period a few times, last year to pencelli castle. It was beautiful, i stood in the icy crispy field about 10pm on my own to get some water, the silence was deafening, it was amazing, i could hear the ice forming on the ground. a very surreal experience.
I also went to Poston Mill once over new year, beautiful site and the most clear air you can imagine. it snowed up here once too, its beautiful waking up, rolling up the blinds and seeing a white landscape from the van.
Do it, its wonderful.