Check out this link. Lowrance has a mount to attach the LSS-1 to the trolling motor, curved bottom for a flush mount.
I have an HDS 8 up front, couldn't go $600.00 more for a 10! You will need two black boxes since a module can only run one transducer. In my opinion get the LSS-1 for the front and get the largest HDS you can afford. If it's only a 7 that's where to compromise and later upgrade to a bigger screen unit. The Structure Scan on the front is more important information for me while I'm fishing than the size of the screen.
I don't know many people who put them on their trolling motor yet, but that's OK to me since it gives me an competitive advantage although it hasn't paid of yet, but it will.