On my previous coach, there were seals around the slides that were suppose to flip outward when the slides extended. They didn't always do that. I used my awning rod, slid it under the seals and flipped them outward.
On our previous coach you could feel some drafts, usually around the bottom and lower edges of the slide. We would place a towel along the edge to stop the draft.
Make sure your dash vent controls are all turned to the off position. Often, if they're in the vent mode or other position, it can let outside air in. Your windshield is a huge source of heart loss. You might hang a blanket in front of it, using the visors for support.