I've got two 20" GT 200s which I can dual mount and two Merc 275-Coswoths which are 20 & 25". I thought I could mount the 20" mids right on the transom and maybe mount the 20 or 25" on a transom bracket and or a jackplate. My mech told me that he believes I need a 30" to mount as a single and 25" to mount twins, is this so. I know airdog mentioned that I use the transom bracket he used, 24" heavy duty. But I'm not sure how that would look W/O closing the motor well, which I hear is a lot of work.