Good question. It's always a safe bet to use the isolation gasket set when installing them on an aluminum boat. The GM400 composite mount does have a stainless plate on the bottom side that retains the latch and spring mechanism. While it is slightly recessed from the bottom surface of the mount, it could still come in contact with the surface of the boat. Another advantage to the G410 isolation gasket is that there are small 'protrusions' on the gaskets that keep the ¼-20 stainless hardware from contacting the aluminum hull material as well.