Norcold refrigerator very slow to cool down.

I have a full size Norcold refrigerator in my 2008 Journey. It is stored year round indoors. Before leaving on a trip, I turn on the propane and turn on the refrigerator about 24 hours prior to departure. When we leave, the inside of the refrigerator is still at about 70 degrees. If I turn the generator on and run off of AC, the fridge cools down much faster. I notice that the propane does just fine once the fridge has cooled down. I have had the system checked and there are no leaks. Is it normal for propane to take such a long time to cool the fridge after sitting at outside temp for an extended period of time? Any insight would be appreciated.