Did similar after visiting Phoenix one day and flying with Rusty Fried.. he had a similar cooler - I just improved on it a little.. in my opinion. Shown my self contained system. The TP5300 battery sits on top of the 12v battery such that the narrow side of the battery rests on the 12v battery - allows air flow around the battery and between the 2x 5300's. Rusty sells these fans as part of his boat store misc items.

Here are the fan specs - really pushes the air !!

Patented in-line design – provides ventilation for engine compartments, galleys, bilges, and heads. Mounting feet allow vertical or horizontal installation in confined spaces. Install with #10 fasteners. Individual carton includes 2 tie straps. All are CE certified. 16-gauge tinned and caulked copper wire leads with optional MP1 molded rubber connectors. New improved 3" design includes:

145 CFM Open Flow
3.1 Amps
3" hose
Nickel-plated motor can for corrosion resistance
Stiffening ribs to reduce housing distortion
Motor cap to seal wires and motor for water resistance

and a link to the fan.. this is not Rusty's store.. http://www.boatersland.com/att17314.html

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