Hi Sam,
Material Manager
>New Material
>Select Texture 2D from the shader selection
>select your "Mask" image (something with an alpha dissolve to it.)
>Layer 1 of your material
>Blending
>Change source = ZERO
This will make that image a mask image.
Apply to a quad, and you now have a mask.
Masks will only mask objects behind it (z-axis)
So place this quad in front of your lower third (or everything you want to mask)
If you need this two wipe on, just animate this quad.
Hope that helps.
Let me know how it goes.
#Carbonite