How to apply style trigger to datatemplate in WPF - wpf

Question

I've got the following..
<ComboBox Grid.Row="2" Grid.Column="2" Grid.RowSpan="2" ItemsSource="{Binding ShipperAddresses}" Text="{Binding ShipperAddress}" Margin="85,2,0,2">
<ComboBox.ItemTemplate>
<DataTemplate>
<TextBox AcceptsReturn="True" Width="200" Height="100"/>
<DataTemplate.Resources>
<Style TargetType="{x:Type TextBox}">
<Setter Property="IsReadOnly" Value="True">
<Style.Triggers>
<DataTrigger Binding="{Binding RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type GroupBox}}, Path=Tag}" Value="False"/>
</Style.Triggers>
</Setter>
</Style>
</DataTemplate.Resources>
</DataTemplate>
</ComboBox.ItemTemplate>
</ComboBox>
The problem is that you can't apply a Style.Trigger like I'm trying to do inside a DataTemplate. So my question is how would you apply create a trigger so that a property on the DataTemplate changes based on the parent?
FINAL SOLUTION:
I took what Souvik gave me and fixed it up since there were a few problems. Here is the end result.
<ComboBox Grid.Row="2" Grid.Column="2" Grid.RowSpan="2" ItemsSource="{Binding ShipperAddresses}" Text="{Binding ShipperAddress}" DisplayMemberPath="Value" Margin="85,2,0,2">
<ComboBox.ItemTemplate>
<DataTemplate>
<TextBox AcceptsReturn="True" Width="200" Height="100" Text="{Binding Path=Value}"/>
<DataTemplate.Triggers>
<DataTrigger Binding="{Binding RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type ComboBox}}, Path=IsEditable}" Value="False">
<Setter Property="IsEnabled" Value="False"/>
</DataTrigger>
</DataTemplate.Triggers>
</DataTemplate>
</ComboBox.ItemTemplate>
<ComboBox.Resources>
<Style TargetType="{x:Type ComboBox}">
<Setter Property="IsEditable" Value="True"/>
<Style.Triggers>
<Trigger Property="IsDropDownOpen" Value="True" >
<Setter Property="IsEditable" Value="False"/>
</Trigger>
</Style.Triggers>
</Style>
</ComboBox.Resources>

Answer 1

Have DataTemplate trigger instead of Style trigger:
<ComboBox Grid.Row="2" Grid.Column="2" Grid.RowSpan="2" ItemsSource="{Binding ShipperAddresses}" Text="{Binding ShipperAddress}" Margin="85,2,0,2">
<ComboBox.ItemTemplate>
<DataTemplate>
<TextBox AcceptsReturn="True" Width="200" Height="100"/>
<DataTemplate.Triggers>
<DataTrigger Binding="{Binding RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type GroupBox}}, Path=Tag}" Value="False">
<Setter Property="IsEnabled" Value="False"/>
</DataTrigger>
</DataTemplate.Triggers>
</DataTemplate>
</ComboBox.ItemTemplate>
</ComboBox>