A USB port produces 5 VDC, not 12 VDC. Most USB ports can provide a max of an amp or two. This, of course, is nowhere near what you need.
Trail Manors used to have a cigarette lighter outlet similar to the one in the picture. This is what Shane was referring to. It could supply 12 VDC at about 8 amps max. If you had one of these outlets, you could plug the small DC compressor refrig you mention into it, but the outlet is on the edge of being inadequate for an 8-amp load. The other downside of these things is that they tended to overheat when run near their max rating. Bad idea.
If you buy a refrigerator that will operate on 12 volts DC, you could have it hard-wired into the TM electrical system. Not a big deal, since the required connections are in the back of the refrigerator cubby.
If you buy a refrigerator that will operate on 120 VAC (house power), you could plug it into a normal household outlet when AC power is available at your campsite - again not a big deal since there is an AC socket in the refrigerator cubby. Or you could buy a small inverter (maybe 200 watts) and use it to run the refrig on 12VDC when AC power is not available.
But USB is not an answer.
Bill
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