Not in January, but we were in Death Valley in mid-November. Day time temperatures were still decent; chilly out in Pahrump where we stayed and DV itself was nice (mid-70s during the day). Night-time temperatures were chilly- 50-ish, if I recall correctly. I'm not sure how that changes for January, of course.
I don't think I'd stay in Pahrump again if I had a choice. Nevada Treasure RV Resort was stunning and we loved it there; but the drive to the edge of Death Valley was pushing an hour. Then you had up to 60-90 more minutes depending on where you were headed.
I wanted to stay at the Furnace Creek campground where they have hookups, but happened to try to stay over Veteran's Day and they were booked up. We can't go without electric hookups (at least- never mind my issues with lack of water or sewer). So we stayed outside of the park.
If you do stay over in Pahrump, consider checking out Dublin Gulch. It is crazy to think that people lived in the caves up until 1970 or so. The garbage left behind and modern-day litter is heartbreaking.
Pics from our visit to the area: