Make a Dynamic Component. 3D text component with its axes centered in the component. Position of the text set to 1/2 the overall length (LenZ) of the box and 1/2 the width (LenY).
90% of the process is in Sketchup. Between the initial design, showing to the client, finalized design, showing to the architect & builder, there’s a lot of benefits in having such symbols and framework items in Sketchup, before we arrive to the last step in Layout.