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Currently doing the same thing, except for 3 weeks and we go from Kristiansand to Trondheim to Oslo in a large circle. Did the Preikestolen hike 2 days ago, be sure to go early as there will be A LOT of people if you go too late.
We try to camp as much as we can in the wild but in crowded area's like Bergen where I'm currently staying it's hard/near impossible to find a decent camping spot near the road. Because we have normie quechua 2 second popup tents and no light camping gear at all we can't hike to a decent location. I would definitely recommend packing light, it's what I will do on a next trip.
Also, check out the park4night app, it's targeted mostly at RVs, but you can check out some cool free camping spots which people share. Pic related is where I slept last night