Check out the Nav+ card if you are wanting to get multiple areas. The way that is works is, you purchase the card and it is preloaded with all of the US with premium data, once you plug it into your computer to update, it will ask if you want to purge that data. In your case you would purge the data and draw boxes around the areas you would like to fish. Check out the free webapp so you can viw your areas before making a purchase:
Here is an example of Toledo Bend for lakes:
Be sure on the Webapp to toggle the button in the bottom left to turn on the Sonar Charts layer!!