I have a very large HVAC air return in my living room that requires a 36x12x4" extended triangular baseboard diffuser (old house). I have not been able to find anything that fits the bill and the old one we ripped out was a built in wood one that was full of mold. Is there any reason why we couldn't install two 18" ones immediately adjacent to each other (with the correct support underneath to make sure they don't fall through the center)? Thoughts? Has anyone done this?