Haven't tried it, as it is very soft (more of a med to hard cheese smoker, myself...much more forgiving), but you'll want to cold smoke...40-60*...else it will turn your grates into a cheese slicer and melt away and slide through your grates...probably if it gets much over 70-75*. Velveeta is already processed, so it's been heated and stirred to death...doesn't take much heat to get very soft and eventually to the melting-point. Also, if you have jerky grates, they will help support the cheese better than heavy wire or expanded metal grates will.
In the colder winter temps, you shouldn't have any issues keeping your smokehouse that cold. One note: cheese takes on smoke slower in colder temps, so 6 hours may get what you want. Harder cheeses I've smoked around 100* were pretty strong after 4 hours. Warp it up and toss in the fridge for a couple weeks to allow the smoke to mellow and absorb into the cheese...then it'll be ready for proper enjoyment.
Eric