I have a Lowrance HDS 5. I have the navonics charts for it and the base maps. The maps for inland waters is not good at all, what are my options for getting topo maps on this GPS. I have searched high and low and can not find topo maps for it or any other marine GPS for that matter. I was wondering what everyone else was using. I take a hand held with me but that is not ideal. Thanks for the input.