There is the general hut, which is open to everyone, right on the hiking trail and, a little more hidden in the forest, about 500m away, the hunting and fishing association's hut. The general hut has 4 beds with an oven and cooking facilities and the firewood is in the boat shed 100m and there is a really ugly, disgusting outhouse. The hut is sufficient for one night, but it can happen that it is already full because you don't have to register and it is busy seasonally.
For the other hut from the hunting and fishing association you have to rent a key in advance, but the hut is a little more hidden in the forest, on its own lake, has 3 beds and is better equipped with a gas cooker, oven, dishes and blankets, solar system, etc. and has 2 own boats to use for fishing and own firewood and a much better, clean outhouse. You can get the key from Emil on this page njff.no/nordland/fauskeogsorfold/hytter?accordion_section=4-2&#accordion_section=4-2,
Simply email him in advance from Germany and then meet him in Straumen before the hike. Paying by credit card works great. It's definitely worth spending the few euros.