To the OP,
1. What you did helps, but the refer needs to be pulled and the CU pulled and the Transfer Mastic installed correctly
2. There is NO WAY you can tell in the freezer the condition of the Transfer Mastic. You have the pull the CU to tell
3. From your long explanation---The CU was NOT installed correctly.
4. I ALWAYS advise customers to replace both fans and the tstat for the fans when I do a 1200 series CU. I also run a 2 wire jumper from the tstat to the back side so test the fans or even have the fans run all the time to get better cooling in cooler climates.
5. IF the CU is NOT sealed correctly, in transit, the refer will heat up. The refer can actually PULL in hot air while the RV is in transit if the CU is NOT sealed at the back correctly. Will work fine camped. Doug
PS, yes, that shop would NOT like the Amish CU if they do not install them correctly and will blame the Amish Junk, instead of their own incompetence when customers complain