Mars Odyssey hydrogen-content measurements have shown seasonal deposition of water/ice on Mars even at equatorial locations. This has been confirmed by the Opportunity rover in Meridiani by the observation of early morning frost on the rover:

More on "Frost on the rover solar panels".
http://bautforum.com/showpost.php?p=323577&postcount=6

This deposition of frost at Meridiani corresponded to the observation of clouds over the site during the local Winter:

Mars Rovers Spot Water-Clue Mineral, Frost, Clouds.
13-Dec-2004
http://marsrovers.jpl.nasa.gov/gallery/press/opportunity/20041213a.html

Since clouds have also been seen over the site during the current Summer season, I argue this should also correspond to water/ice deposition currently at the Meridiani landing site:

Space Sciences
Summer clouds over Meridiani?
Posted by Robert Clark on 12/31/2005 6:56:40 PM
http://habitablezone.com/space/messages/409185.html

The "Mars Rovers Spot Water-Clue Mineral, Frost, Clouds" press release showed the frost forming in early morning in the Winter season. The image of the frost was taken 11 minutes after sunrise, and a subsequent image showed the frost had burned off 3 hours later due to rising temperatures.
Perhaps the clouds in the images in the current season appear at night because of the coldness at night during this current Summer period. Then we might expect the greatest water/ice deposition to also occur at night.
Could the mini-TES detect H2O on the rover at night? Could we for example compare the spectra at night to the morning spectra?
Another experiment I suggest to try would be to press down with the RAT at night and keep the area covered till early morning. Then uncover the area soon after sunrise to see if there are any remaining signs of moisture.
This may have what occurred at the Gusev landing site with the Spirit rover landing bags with the observation of the "magic carpet" mud-like material. The Gusev landing occurred within the period that the Mars Odyssey readings showed the greatest water/ice deposition occurs during southern Summer. Then the landing bags covering the soil may have allowed deposited water/ice to be retained against sublimation/evaporation. When the bags were pulled away, moist soil would have been revealed.
That this deposition occurs may provide a means of obtaining water for consumption or fuel (hydrogen through electrolysis) by future manned missions. The method of a "solar still" allows water vapor in the air to be collected and condensed to liquid water even in desert regions:

Desert Survival
Collect Water in a Solar Still.
http://www.desertusa.com/mag98/dec/stories/water.html

Bob Clark