Hi Halbe,
I have some great experiences with fishing in Lillebælt. Normally, when I have fished in Lillebælt it's in the cities Middelfart and Strib. In Middelfart they have a great place at the harbor (there is also a fishing store near the harbor - look it up) and in Strib you should try to fish around Strib Fyr (in english called Strib Lighthouse).
Hope I could help you out!