I can't answer to how the weather is in February, but I can tell you in late November, it's still warm/cool in the day and cold/windy at night. It's actually been nice when we were there in November.
As for a Class A, you can get pretty far out there as long as you're on the main (washboard) road. You will notice most of the Class A's are around the main road (right off the main road going North toward the park), because the ground is packed hard. As you move off the main road going West or East on the washboard road, you will be fine. It gets tricky when you're finding sites off this road where the ground can be soft. I was able to get a family member's 35ft Class A about 2 miles West of the main road, but the ground was still soft moving around, so we did have concerns of settling and getting stuck. Fortunately, we didn't have an issue. Use a scout vehicle if you have one and looks for well-used sites where the ground is packed. It can be done, but don't take unnecessary risks.
Good luck!