Hi Mateusz,
what kind of IBase component do you want to create? As you mentioned the IS-U connection object I'd expect a premise or a PoD.
If this is the case have a look at the component IUICOBJ. In the EH_ONADD method of the view IUICOBJ/SOToolbar you can see how to use templates to create connection objects, premises and PoDs. If you don't want to you templates, have a look at CL_CRM_IU_IC_OBJ_CUST_TMP=>HANDLE_TEMPLATE. There you'll see how to create the different objects.
Christian