Reading about this pilgrimage i discovered that free camping is allowed in Norway so i searched for a light tent since accommodation prices are a bit high. My tent just weighed 1 kilo.
Sleeping under the stars can be hard on the mountains, even in summer the nights are cold. The first night i pitched my tent, on the Dovrefjell before the Ryphusan's refuge, i didn't sleep at all, it was cold and there was a high humidity in the air. The tent got wet inside and i didn't want to use my sleeping bad as it could get wet aswell. I just used the tent one more time, before Skaun.
At camping places i got cabins. I should have used the tent but... cabins were so cute...
I remember the weather was hot in those places at the sea level but cold and wet (not rainy, though) on the mountains. Some locals told me that that was a wet August, maybe this year will be different. I just walked under the rain one day, and it was light rain, near Rennebu.
Are you going to walk from Oslo? Perhaps you can sleep under the stars before reaching the Dovre mountains but over them you will need a tent, a good and waterproof one.
Anyway, you'll enjoy it. You'll see.
PS: Sorry, i don't have a blog.