Как создать DLL, содержащую форму?

сборка dll:
.............
namespace testform
{
    public partial class FormDll : Form
    {
        public FormDll()
        {
            InitializeComponent();
        }
    }
}
.............
приложение
Assembly assembly = Assembly.LoadFile("C:\\prg\\testform.dll");
Type type = assembly.GetType("testform.FormDll ");
Form form = (Form)Activator.CreateInstance(type);
form.ShowDialog();