Yes, the main road from Bergen to Oslo is absolutely no problem. There are very few roads where a caravan would be inappropriate and most of these are minor roads.
If I were you I'd get a road map from the Norwegian Tourist Office. They issue (or at least they used to) a free one with all roads marked which are unsuitable for towing or which require some experience. Most were in the fjord country north of Bergen, towards Trondheim (lovely country, so still worth a try).
Our very first experience of caravanning was touring Norway and I found that even those roads marked as unsuitable (and there weren't many) were negotiable for a novice so long as the caravan is not too large and one takes a bit of extra care. In cases like that one must be prepared to perhaps have to reverse the outfit a few yards to a passing place if there is wide oncoming traffic.