How do I prevent the Designer-Grid from being drawn on my Container Control during design-time?

You can do so by overriding the DrawGrid property in your custom designer:

public class MyContainerDesigner : ParentControlDesigner
{
	protected override /*ParentControlDesigner*/ bool DrawGrid 
	{ 
		get
		{
			if (!this.disableDrawGrid)
				return base.DrawGrid;
			else
				return false;
		}
	}
}