........I use a system of not covering the vents but restricting the air flow through them.
To that end I fit the restriction inside the vents.
The restriction I use is the plastic foam material of the sort that is fitted behind domestic heating radiators. The stuff that is flexible and has aluminium foil on one side.
It's counter intuitive but the whole point is to alow the workings of the absorption fridge to be able to reach a high enough working temperature during ambient temperatures below 6 degrees C.
I need to be able to use my fridge with the restrictions in place during gas operation so the top vent is sized so as not to restrict the burner exhaust.
I usually fit the restrictions when towing with the fridge on 12volt operation as the airflow across the vents can also over cool the fridge workings and affect its cooling efficiency.