I'm with Clark on this one. I've done this many times (support a structural ridge with kingpost trusses). It's one of my favorite structural approaches.
Specific to your frame, the heel joint where the top chord of the kp truss joins the bottom chord is the Achilles heel of the truss design. With such a low pitch, the thrust is magnified. It will take a lot of bearing area at that joint to transfer the load, and it will take a lot of shear plane in the relish between the bearing area and the end of the bottom chord to keep the force from splitting off the end of the bottom chord. And at that point you've taken a bit of meat out of the BC and it needs to be able to take the downforce of the truss and transfer it into the post without breakig. This is what Mike is talking about in the post above. You'll need a stout bottom chord for this reason.
But back to Clark's recommendation -- have an engineer work with you to design the connections. I always do.
