The ONLY thing on a RV Fridge that is insulated pipe is the 'burner stack'
Gas burner on bottom and electric element in tube welded to side.
Heat (350*F gas flame/330*F electric heat) ....liquid ammonia rises being heated
The Flue/burner stack/perc tube are wraped in insulation and then covered by sheet metal.
Any other 'insulation' falling down would be insulation used in side walls/roof of fridge enclosure cabinet.
This is a new cooling unit .......not installed..........burner stack is on right side
Not sure what insulation you are having to put back on??????