Scenery Transparencies

I've had it in mind now to learn how to do transparencies in scenery to make them more realistic.  One application for this is more complex scenery with things like handrails etc.  To do this with vertices is possible but very inefficient when a flat plane with transparent areas can be used.

I've sorted out being able to use alpha channels with textures, and as you can see have managed to get transparent textures into Sketchup now.  The red area to the left is a large red box inside the model :)

I'm having some problems importing them into ModelconverterX though so actually using them in FSX isn't possible at the moment :(  Little by little though I'm getting there....