The most common cause of Heat up in Transit is the evap tray hose check valve not in place at the bottom of the hose. While you have a fix, it was not needed. I have NEVER in the 25 years of the Norcold 1200 series ever had a problem with in Transit heat up that could not be a simple fix. If I did have that problem it was traceable to either that drain hose or the Interior door seals. There is a natural vacuum caused to the refer while in transit. GOOD door seals and the Drain hose not open to the exterior fixes the problem. Doug