The US has about 300 million citizens (and possibly some 30-50 million illegals on top of that) compared to your 4.5 million. So if the numbers were comparable, we'd have about 13,333 families living aboard, not 205,000 people unless I've done the numbers wrong with a metric conversion.
I doubt we have that many but counting the various houseboat communities it certainly might be possible, or at least half of it might be possible. Bear in mind that compared to Nroway we have a much shorter tradition of very much cheaper land and very much larger farmsteads and estates. Why our women would want to be cooped up in small spaces like boats, when they've been promised a white picket fence and house all their own, I can't begin to guess. I suspect that if Norwegian women were offered the same options--you might have a lot of unhappy men selling off their boats!
Compared to your 307,400 sq. km. of territory, we have just under 9,162,000 sq. km. of land, 29 times the land mass and way less of it split up into islands or mountain fjords. Then again...we also have a lot of ex-Norwegians scattered about, perhaps the ones who didn't want to live on boats all came here?