Ideally you should take a compass and put it all around and see if there is any interference around where you want to mount it. I put mine up front on the little tool holder so I did t have to screw it to the boat.
This. I was shocked at the level of magnetic interference at the bow and by the driver’s console. Too many electrical wires it seems. Get a cheap compass and move around your boat to find the best spot. Mine was on the back deck, passenger side.