Steel CONEX containers would be the perfect mouse shacks, if the sun didn't have a habit of turning them into gigantic ovens. But with a little ingenuity, a small air conditioner, and a reasonable amount of insulation you can quickly turn that oven into something cold enough to store meat in, even in the Texas sun.

CONEX boxes are available in many different types and sizes from gigantic 40-foot monsters down to tiny 6- or 8-foot units. Some are designed as cooler units, referred to as "reefers," but most are just giant steel boxes designed to carry goods in bulk around the world as deck cargo on ships, trains, or trucks.

The price varies, but used reefer units are generally out of the reasonable price range with 20-foot units going for $6000-$9000. A standard, non-leaker, used 20-foot CONEX box can usually be located on Craigslist for around $2000-$2500, and can be moved by most flat bed tow trucks a reasonable distance for $100 to $150. Larger, and heavier, 40-foot units usually require a specialized delivery truck, a lot more room, and a lot more money.

We found our CONEX box locally on Craigslist for $2100, and had a tow truck deliver it to our site for $150. Our unit came with passive louvered vents on the front door and the rear, although most do not. Once the unit was in place, we made the first of what would be many trips to Home Depot. There we bought a small window A/C, an inexpensive pre-hung interior door, some 2x4s and a number of 1/2- and 3/4-inch 4x8 reflective exterior insulation panels. And duct tape. Lots of duct tape.

With an active vent louver from Amazon.com and a box fan and a Sawzall reciprocating saw from the shop, we set about modifying the CONEX box. First, we removed the existing vent from the rear of the unit, then we expanded its hole using a metal cutting blade on the Sawzall. Though the steel is 1/4-inch thick, the reciprocating saw had little difficulty cutting though it. Once the vent hole was expanded, we cut another hole below it for the air conditioner. Bracing it with wood on the inside, we installed the A/C, making sure that the intakes were reaching the outside.

The vent hole we started with was larger than our active went louver, so we had to make a 2x2 wooden plate to cover the gaps. Once installed, and tested with a fan, the louvers popped right open like designed. Hooked up to a timer, the ventilation fans will come on from 10 pm to 8 am, automatically opening the louvers and venting the mouse room of any built up ammonia for 8 hours. The louvers will close when the fans turn off and the A/C runs, from 8 am to 10 pm.