The P20 has inner walls that slope inward sothat the base WxL is smaller than the lid opening WxL. It is so small at the base that you cannot seat the all too popular ZipLock square storage containers. It is primarily intended to fit between the front driver and passenger captain chairs in a minivan that has no center console. Additionally, the cooling element protrudes inside the front wall, further reducing the inner space. Cleaning would be difficult since the cooling element and fan must never get wet.
I tried the Coleman 16-Quart thermo-electric cooler. The base is a hair too small to seat two of the square ZipLock containers side by side. The cooling element is built in the hinged lid, which leaves more space for storage. However the fan is noisy.
Finally, I tried and loved the Koolatron P25. It has a very roomy interior, has superior insulation, has the cooling element built into a detachable lid, which makes rinsing the container much easier, and finally has a very quiet fan. The only small negative is the absence of a red LED from the cigarette lighter plug to confirm that cooler is running.