Hi lgc1970. I did keep the humidity in that range -- probably closer to 55 percent average. It is really dry here, esp. when the furnace is running. But I didn't increase the room humidity with a humidifier, and the room temp was closer to 68 average. But the incubator was really stable between 99 and 100 F. I used a Lyon TX6, which is easier to keep stable than the styrofoam one I used last year. Also, another difference was that the eggs lay on their sides in the TX6, and I turned them manually every few hours throughout the day and occasionally at night if I woke up. I didn't have to open the incubator since it has little knobs on the outside that move the egg grid and rolls the eggs. Last year, the eggs were in an automatic turner that just rocked them back and forth. During the last couple of days before hatch, I raised the humidity to 65 - 70. The shipped eggs I hatched this year came from Texas and Tennessee, so they were from much lower elevation, and I really don't think most of the chicks I got would have lived if I hadn't intervened. They are doing great now, though.
If you're going to try it, there are some good threads on here to read about assisted hatches. I was pretty aggressive in making sure they didn't go very many hours after they pipped before I enlarged the pip hole for air if they weren't making progress. My guideline was if I saw any sign of bleeding at all when I was chipping egg shell away, I put it back in the incubator for an hour or so until I got most of the shell & membrane away from the chick's head, and left the bottom half alone, then I put them back in again, and they were able to hatch themselves when they were ready.
Good luck to you! It was pretty nerve racking, but it was worth it since I got the chicks I was wanting. Hatching from my own chickens is much more fun, though!!