[JRTJH]

From your description, "I did check the lower vent while we were camped and without taking the cover off I could feel heat coming from it..." tells me that the "convection draft" that is supposed to carry cool air from the bottom of the "chimney" to the top vent was not working properly. Why? Probably, as you suspect, something to do with the winds against the trailer side. In "normal operation" the airflow should be into the bottom vent, up and through the fins (to exchange heat) and out the top vent (to remove the excess heat). If you felt heat coming out of the bottom vent, airflow was reversed and not proper. Typically, there are thermally controlled fans mounted under the fins to help push that convention current in the proper direction and to increase the amount of airflow. If wind was pushing air into the top vent, and if the temperature inside the chimney was low enough not to trigger the fan operation, that wind could disrupt that airflow and "stagnate" the cooling effect causing the refrigerator to not be able to release the absorbed heat. Sort of a "perfect storm" kind of situation, but likely that's sort of what happened.

Just my guess, but hopefully it was a "fluke" that won't recur.