Small12-volt portable refrigerators offer the comforts of cold drinks and leftovers to the person who is on the road for extended periods. Though most users keep their portable refrigerators in an RV, truck or car most of the time, there are rare instances when you may have to keep your small appliance outdoors in an outbuilding where an AC to 12-Volt DC converter is used to power the unit. Though these refrigerators do have some insulating properties to them, items can freeze if the outside air becomes colder than the interior, which may overcome the unit's ability to keep the internal temperature stable.
Inspect your portable 12-volt refrigerator to locate the ventilation fins on the side, bottom, and back of the unit. Then, using a tape-measure, measure the distance from the edges of the unit to the location of the vents.
Measure and cut square air entry holes into the Styrofoam cooler so the holes match the vent locations on your refrigerator when it is set inside of the cooler. Set the refrigerator into the Styrofoam cooler upright and create another hole just large enough to pass the power cord of the unit through the Styrofoam.
Press fiberglass insulation along the edges and the top, between the refrigerator and the Styrofoam, using a paint stir stick to press it inward so it lines all of the surface area between the refrigerator and the cooler. Use the paint stick to gently move insulation away from the vent holes so the refrigerator vents are visible through the Styrofoam.
Place the Styrofoam lid over the front of the cooler, and use duct tape to secure it in several places so that it is sealing the refrigerator inside. When it is necessary to access the contents of the refrigerator, gently peel the tape away from the sides and remove the Styrofoam lid, replacing it when finished.
