Rigging a mesh with static components

I made a low poly catapult for Unity that has a root bone, a bone to control the winding arm(for adding tension to the catapult), and an ik chain for the catapult arm and bucket. I have it rigged and it works fine in Blender, but when I export it to Unity, it complains that there are vertices that have no bone applied. In this case it is referring to the frame of the catapult.

Is it common practice to weight static parts of mesh to the root bone since it is not a deform bone, or should I create another bone and uncheck deform?