I installed a 3h x 4w window in my drywalled garage wall. It's framed with 2 x 4s and the header, which show--I want to cover them with 1/2 inch drywall and a corner bead for appearance. The depth of the window sill/frame is only about 2 1/2 inches. Do I have to tape and mud these inside corners or can I just run a bead of caulk along them since they are butt joints and the corner bead covers 1/3 their width? I hope the description made sense.