In my opinion, too low is worse. Although shrink-wrap does not happen often, it can. That is why we raise the humidity at lockdown, to avoid shrink wrap. I know you see a lot of posts on here where there is no need to worry about shrink wrap, but every reputable manufacturer of incubators...
What does the bottom of the incubator look like? What material is it made of? Mine has a wire screen so they can't slip. Do your incubator instructions address this? I'm curious as to how big of a risk slipping really is.
The towels being damp would not bother me. If they are so wet that...