Make an object follow another object - silverlight

Question

I am trying to create some kind of a window or a toolbox which can be dragged by its header part, just like any window. For some reason, it doesn't seem to work for me. The header moves but the body part stays still.
Here's my code:
BehaviorCollection behaviorCollection = Interaction.GetBehaviors(this._explorerHeader);
MouseDragElementBehavior mouseDragBehavior = new MouseDragElementBehavior { ConstrainToParentBounds = false };
mouseDragBehavior.Dragging += (s1, e1) =>
{
Canvas.SetLeft(this._explorerBody, (Double)_explorerHeader.GetValue(Canvas.LeftProperty));
Canvas.SetTop(this._explorerBody, ((Double)_explorerHeader.GetValue(Canvas.TopProperty) + _explorerHeader.ActualHeight));
};
behaviorCollection.Add(mouseDragBehavior);
UPDATE:
Here's the control template of the control:
<Style x:Key="ApplicationExplorerDefaultStyle" TargetType="Controls:ApplicationExplorer">
<Setter Property="Width" Value="150" />
<Setter Property="Height" Value="300" />
<Setter Property="CornerRadius" Value="0" />
<Setter Property="Background" Value="{StaticResource LightBlue}" />
<Setter Property="HeaderBackgroundBrush" Value="{StaticResource VeryLightBlue}" />
<Setter Property="BorderThickness" Value="0" />
<Setter Property="BorderBrush" Value="Black" />
<Setter Property="TreeItemTemplate" Value="{StaticResource ChildTemplate}" />
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="Controls:ApplicationExplorer">
<Border BorderBrush="{Binding RelativeSource={RelativeSource TemplatedParent}, Path=BorderBrush}"
BorderThickness="{Binding RelativeSource={RelativeSource TemplatedParent}, Path=BorderThickness}"
CornerRadius="{Binding RelativeSource={RelativeSource TemplatedParent}, Path=CornerRadius}"
Width="{Binding RelativeSource={RelativeSource TemplatedParent}, Path=Width}"
Height="{Binding RelativeSource={RelativeSource TemplatedParent}, Path=Height}" >
<Grid x:Name="Root" MinWidth="100">
<Grid.RowDefinitions>
<RowDefinition Height="30" />
<RowDefinition Height="*" />
</Grid.RowDefinitions>
<Grid x:Name="ExplorerHeader" Grid.Row="0" Background="{Binding RelativeSource={RelativeSource TemplatedParent}, Path=HeaderBackgroundBrush}">
<Grid.ColumnDefinitions>
<ColumnDefinition Width="10" />
<ColumnDefinition Width="*" />
<ColumnDefinition Width="40" />
</Grid.ColumnDefinitions>
<TextBlock Grid.Column="1" Text="{TemplateBinding Title}" Style="{Binding RelativeSource={RelativeSource TemplatedParent}, Path=TitleStyle}" VerticalAlignment="Center" />
<Controls:LayoutToggleButton Grid.Column="2" x:Name="LayoutButton" Cursor="Hand" />
</Grid>
<Border x:Name="ExplorerBody" Background="{Binding RelativeSource={RelativeSource TemplatedParent}, Path=Background}"
Grid.Row="1" HorizontalAlignment="Stretch" BorderThickness="0" >
<toolkit:TreeViewDragDropTarget AllowedSourceEffects="Copy" x:Name="treeViewDropTarget"
HorizontalAlignment="Left" VerticalAlignment="Top" >
<sdk:TreeView x:Name="treeView" ItemsSource="{TemplateBinding Nodes}" Background="Transparent" BorderThickness="0"
ItemTemplate="{Binding RelativeSource={RelativeSource TemplatedParent}, Path=TreeItemTemplate}"
HorizontalAlignment="Left" Margin="10 0 0 0" />
</toolkit:TreeViewDragDropTarget>
</Border>
</Grid>
</Border>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
Any suggestions?