Well first off, you don't use a truss rod to adjust action, you use it to adjust the amount of relief. And since carbon fiber guitars are so stable, a number of builders have decided to make their guitars without truss rods to make things simple. The amount of relief you get is an average level that suits most players.
As for action, you can adjust that all you want by altering the saddle and nut, even if there is no truss rod to adjust relief.
Some of the Rainsongs now come with adjustable truss rods, which is a good thing. But there are many many satisfied players of carbon fiber guitars without truss rods, so it does work - though perhaps not for you.
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