Simple is best. Leave the sides 1/8 or 1/4" proud of the front so the baffle is recessed slightly. Edge-glue a piece of thicker stock to the front that becomes proud of both the front and sides, then roundover. Miter all the edges, then cut slots for splines. Drill holes 3/8 in from each edge 4" apart alternating front and sides then pound contrasting wood pegs into them and sand flush.