Hi Pieter and Kai,
Welcome to Airstreaming! I don't think the Dometic's are dual voltage. Also you will need to do something with your Univolt power converter. Another European member on the board has had issues with his. They are also set up for 120v 60hz. Putting 220v 50hz to them has a tendency to drastically shorten their life span. Check out the Dometic
site for Holland. It has a list of all the neat stuff they make for EU that we can't get in the states.
I would check around with you local RV places to see what they have available for you to convert with. I know there are several other Airstreams in your part of the world and I am sure they had to convert the electrics on them. One that comes to mind is at Route 64
The lady that imported it is Carla Kneepkins and is a member of this forum.
Good Luck and let us know how you make out.