You can stay at a pull off as long as it is not prohibited. We did that last year and had absolutely no issues. The first time no one even pulled in the entire time we were there. We looked for pull offs that had some vegetation between the road and pull off. And we were parked right beside a lake. We did not make reservations but we knew where we wanted to stop each night. We did make reservations for Denali. The Milepost was good to have and also the Church's campground guide. We used it more for the coordinates since many of these campgrounds do not have traditional addresses to input into the GPS. If you can, look for dry camping spots because they are the best ones. Commercial parks have you crammed together slide to slide.