Absolutely go to Yosemite in the snow -- it is beautiful. The only issue would be the size of your rig -- Upper Pines Campground (the only one open) is not great for larger rigs. If you go, make sure you have chains for your trailer as well as your tow vehicle -- they can be required by the CHP at any time.
We have camped in Yosemite in the snow several times. It almost never gets below 25 degrees at night --- Yosemite Valley is only at 5000 feet or so. We have never had a freeze problem at 25. (Fifteen degrees in the Eastern Sierra? Yes, we have had a little problem now and then. ;) )
We did not run the heat at night -- we just piled on the down comforter and several blankets. As a result, we slept in until 8 am, something we never, ever do at home. When you reach a certain age, sleeping well is a huge luxury.
Here is what our campsite looked like in December of 2015:
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Click For Full-Size Image.
And here is a link to a blog post -- lots of photos:
Yosemite in the snow