The skylight is sweating heavily. Lots of condensation in the morning.

Heat more. 18 degrees room temperature and frozen seal says it all ... And then air out as much as possible.

Hello. More than 18 degrees is not possible in this small sleeping room. A single person heats the room up to 20 degrees during the night. And the air becomes increasingly dry when heated above 18 degrees. Already tried everything. You also have to be able to sleep properly. Airing is done regularly during the day - shock ventilation. At night people sleep. Windows closed in winter, because otherwise there would be drafts!

Sleeping with the window closed is out of the question. Even in winter.

But it works very well.

So, I will now try the following.
Heat the glass gently overnight from the inside at the glass edge using a heating tape.
I will mount the heating tape on a styrofoam board all around and crosswise from the inside, and then clamp it onto the glass (between the frame).
This way, the window should warm up slightly and can no longer freeze from the inside.
Emergency solution for this winter.
Let's see if it works.

This way the window should warm up slightly, and then it can no longer freeze from the inside.
Emergency solution for this winter.
Let's see if it works.

And after the winter? In the end, these are all symptoms being fought, but not the causes (=window too poorly insulated). Why not spend some money and replace the window? Then all the tinkering with heating tapes wouldn't be necessary...

Sounds like winter in the camper van (box van). The windshield is full of condensation behind the blinds in the morning. Wipe it off and that's it - works the same in the house. If the window is worn out - replace it with a better insulated one - as long as the dew point is not below a wall.