Let's put the party back at the camp. You'll remember that Lothar did come back from Stavanger TODAY, the 30th of April, before your heading out to the dungeon. It is about 4 in the afternoon when you return to camp ~ and it is raining again. It is what you would just a moderate rain, more or less what you equate to a firm, steady and not unusual rain, much more than a drizzle or a trace.
We had established that 1 mm of rain per day would be enough to cause damage in the wilderness, from cold and general unpleasantness. Since the temperature right now is 4 C/39 F, or "brisk," this makes travelling overland in Norway a real horror show. As you're walking, you'll all take a point of damage on your way back to camp.
We also established that the rain will ensure that you won't get any rest so long as it rains to this degree, regardless of your tents. I've been in many a tent in positively vile conditions in the Canadian Rockies and I can tell you from experience, it isn't restful. Nor was that in a 17th century tent.
You might want to consider returning to Stavanger as a group. You don't know how long the rain will last; it could be clear tomorrow or not. You could get back to Stavanger tonight, with Lothar's help (4.5 hours travel), before the sun actually sets ~ but it will again be a thoroughly miserable trip through a wet forest, no doubt causing more damage (but not enough to kill anyone). You could remain where you are and hope for the best, but cooking in this weather won't be any more pleasant and even if it is better tomorrow, everything will still be soaking wet until mid-day. That will increase the chance of all of you catching a cold, if you're not in a very warm place before then.
And it could always get worse.
Fjall and Valda did not get any rest, nor hit points, today; but they haven't lost any yet, either.