Plugging up the dead spaces around the top and sides of the refrig. is all about minimizing heat gain into the cold boxes from hot environments. Air that can move is air that can gain heat from the outside and transmit that heat to the refrigerator box. The ammonia absorption refrigerator manufacturers even want little dead air volume behind the units, but do want a 0 to 1/4 inch space behind the cooling unit fins. They want the rising outside vent air which accomplishes the heat exchange from the cooling unit to go smoothly upward (the comparison to chimney air flow has been frequently used in this topic in the past), WITHOUT this upward airflow having much of a chance of taking a bypass route near the refrigerator compartment outside wall and therefore NOT DOING ANY HEAT EXCHANGE WITH THE COOLING UNIT FINNED COMPONENTS. The main type of RV ammonia refrigerator installation, in non-slideout motorhomes and trailers, has a straight-to-the-roof -chimney type of installation. You hear about a lot less problems with these refrigerators, than ours in slides with lower and upper heat exchange air vents.
Just on the subject, I have been fighting the above 100 degree daily temperatures for a couple of months here in the California Central Valley (it has finally cooled down some in the past 2 weeks). I had been having daily summer problems keeping the refrigerator below 40 degrees in the heat of the day, even with my tactic of moving 2 frozen blue ice big blocks into the refrig at noon, and back to the freezer at about 10 pm. This was all with the cool control at maximum, and the temperature controlling thermistor at its highest (warmest sensing) position. Anyways, about 4 weeks ago in the same thermal conditions I had been going through all summer, the refrig/freezer temperature suddenly dropped to where I had to put the control setting at its midpoint to keep the refrigerator box above freezing. I can only guess that maybe a partial clog in the ammonia plumbing cleared itself in this 10 year old refrigerator, and it started working better. Everything else on the refrigerator system (outside fans, inside fans, thermistor position, circuit board thermistor adjuster potentiometer, door seals) was the same as before. And, oh yeah, this rig hasn't moved for 15 months.
Crossing my fingers that this holds up.
