Exactly Mike. For instance, a thick closet dowel, or even a 2 X 4, spanning the open cavity of the W-frame, glued to the inside of the two side walls right at the middle (in height) of their front edge. What one could do, for more extreme bracing, is drill holes in each side panel for screws to secure a full depth brace, and install the brace after the front driver is in place. Except that brace might load the front of the woofer slightly (the woofer would fire at the full depth brace at an angle of 45 degrees). Of course, the cavity of an H-frame also loads the woofer to a degree.