Just create a custom control, let's say UserControl1 and add everything you need to that custom control.
VERY IMPORTANT: please set a minimum size to your control.
After this just to the following:
var control = newUserControl1();
// make changes to your control here as needed
var element = newRadHostItem(control);
element.MinSize = control.MinimumSize;
radCarousel1.Items.Add(element);
Hope this helps, if you have any other questions or comments, please let me know,