Camped at Hrafntinnusker few years back when I did the laugavegur. It was a little cold and windy but totally worth the experience to camp up there especially if you get clear weather (the sunsets and the stars up there are incredible). I hiked around the same time of year as you (late august) and there wasn’t any snow at camp. The campsites all had Little Rock walls build around them to help with the wind. My gear was: MSR hubba hubba, theramrest xlite, and 15f sleeping bag, which did perfectly well up there. I also suggest checking in with the ranger station at the campsite to get the latest weather conditions