Ice Box or fan cooler

Hi,
Currently we have an Ingel fridged 32lt set up in the back of the rig, on a slide,all is great with this unit.

However my wife likes her vegatables and our last two High Country trips, lettuce,carrots,tomatoes etc, simply did not last long even though they were individually wrapped and stored in a carboard box.

We also found that the bread went moldy before use also.

So to gain some extra cool storage facility what are people's experience.... If we get an ice box, is that only good for 2 or 3 days?

Also now available($199... 45lt) are these Waeco, fan coolers that work off the cigarette lighter, they drop the temp 15/20 degrees from the ambient temp...I note that they need to be off when the rig is stopped as they draw heaps of power...so I have no problem having such a unit linked to the ignition.

We are doing an 8 day crossing of the Simpson along the Hay River in July, so evenings will be cool....just need a bit more capacity to keep the extra food from spoiling.

Any suggestions?
Regards
Joe