If not using the camper, I would think slides In. If you're actually using it, slides out. I'm keeping my slides in and pull them out when we use it (on weekend driveway camps). We had some light snow a few days ago and the slides were out. It also got really, really cold and I wanted to button up the camper and sleep in the house. Then it dawned on me, I had to get the snow off the slides (I don't have a topper on any of them). Luckly, the snow was power-puff and my leaf blower blew the snow off and I did it early enough in the morning the morning sun did not have a chance to start melting it. Then I put the slides in and they've been in ever since.
If you plan on using the camper, I think it's OK to leave the slides out, but if they are out and it snows or rains and it freezes to the tops of the slides, and then you want to put the slides in, I don't think that frozen water on top would be good for the seals, or the possibility of all that water melting and dripping on the inside of the camper.
Our light snowfall made me stop and think long and hard. We're planning a trip to Florida over Christmas. The last thing I want is to have the slides frozen OUT and couldn't get them back in because of a mountain of frozen snow, ice, water on the roof of 3 slides!