The rack shown on the '82 245 Turbo will come apart, then the side rails will flop over. They're hinged. The later racks, used on 1983 and newer cars can be used as roof rails, instead of a roof rack, though. The feet are solid metal, so they don't flop around. Ideally, if you're going to go through with this, I'd find a 1991 240SE wagon to pilfer the roof rails off of. They're very similar to what's used on the 960's and late 940's, but for a 240.
With respect to my comment about rust on the roof, it happens even on cars that are mainly in dry climates. Case in point, my 245 (the one on the far right in the signature pic) came from New Mexico. It still had rust on the roof when I removed the rack. Only surface rust, but still, it had rust forming. I was able to stop it with some POR-15 paint, but will be doing a more permanent fix this summer, while getting the roof and the hood repainted. Will do the same fix on the wagon in the middle, which also had a rack on it originally.
One thing to think about, is how often is it actually dry, warm, and sunny during the summer in Norway? If it's that way for the whole time you'd be driving the car, then you might be ok. If not, then you'll definitely be dealing with eventual rust issues and water leakage.
-J
