One set of 8 lithium batteries will supply 3000mAh of current.  You are looking at taking 4 sets that would be 12000mAh of current. I see 2 other options.
Option 1:  4 X 8 = 32 Lithium batteries 12000mAh. $60.00 for one trip 14.6Oz
Option 2: 5 X 10 = 50 Duracell Quantum Batteries 12000mAh. $20.00 for one trip 2Lb 9Oz NOT COPPERTOPS
Option 3:  3 three cell Lipo 5000mAh battery packs 15000mAh $80.00++ for many trips 3Lb 3Oz
The Lipo battery pack I was looking at is at the following address.
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Notice that the cost of Option 3 is $80.00++.  The ++ stands for the extras you need to not destroy the battery.  Lipo batteries require special chargers so as to not over charge any cell. I believe the following charger is one that would work $25.00
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Lipo batteries require protection to prevent any individual cell from being over discharged.  There are 2 readily available options for protection boards. 
Protection option 1:  Is easy to hook up.
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All it does is sound an alarm and turn on a LED when any cell goes below 3.3 volts. You can still leave your fish detector on and destroy the battery. But it is easy to hook up. If you leave your detector on overnight or while you are away from your canoe and the battery goes down it will destroy the battery. But it is easy to hook up.
Protection option2: A circuit that opens up a switch and shuts the power off to the fish detector when any cell goes below 2.4 volts. $10.00
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This does not come with connectors and must have leads soldered to the board.  The connectors can be gotten by buying some adapters form Hobby king and cutting the connector off that you need.  I have charged through one of these boards and it will protect against overcharging preventing the destruction of the battery but it does not balance the charge reducing the battery capacity.
Let us know what you decide to go with.