If you have an OnLoad you can set the backdrop there:
Lua Code:
<Ui xmlns="http://www.blizzard.com/wow/ui/"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
<Frame name="BCHFrame" parent="UIParent" toplevel="true" movable="true" enableMouse="true" inherits="BackdropTemplate">
<!--Anchors is a property element-->
<Size>
<AbsDimension x="200" y="150" />
</Size>
<Anchors>
<!-- An anchor can be created with frame:SetPoint() method-->
<Anchor point="LEFT" relativePoint="CENTER">
<Offset>
<AbsDimension x="150" y="0" />
</Offset>
</Anchor>
</Anchors>
<Frames>
<!-- close button -->
<Button name="$parent_CloseButton" inherits="UIPanelCloseButton">
<Anchors>
<Anchor point="TOPRIGHT" relativePoint="TOPRIGHT">
<Offset>
<AbsDimension x="0" y="0" />
</Offset>
</Anchor>
</Anchors>
</Button>
</Frames>
<Scripts>
<OnLoad>
self:SetBackdrop(BACKDROP_DIALOG_32_32)
self:RegisterForDrag("LeftButton")
</OnLoad>
<OnDragStart>self:StartMoving()</OnDragStart>
<OnDragStop>self:StopMovingOrSizing()</OnDragStop>
</Scripts>
</Frame>
</Ui>