You could call for both designs by name in the file. You could also put them in the UnitConstruction (or whatever the name is) file, but they won't be built until the queue in VehicleConstruction is completed.
Are the designs in your DesignCreation.txt file in that order? I thought the AI always built the first design it found which it had sufficient tech to build. I have been wrong before, though.
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The Unpronounceable Krsqk
"Well, sir, at the moment my left processor doesn't know what my right is doing." -
Freefall