I've been struggling with a similar issue. I think I've boiled it down to outside temps.
When I bought the trailer, it was in the low 70s. The fridge was in the 30-40 range, the freezer was 20-30 range.
Had it plugged in and running ever since sitting in my driveway. When I checked one day, I was shocked to see the fridge skyrocketed to 70... however the freezer was still good to go. The outside temps were 85-95 however.
Then on a Sunday we had a storm blow in, it went from 95 to the low 50s! I checked the fridge and it returned to the 30-40 range. Then back up to 70 when the heat got back up.
I'm researching getting some cooling fans for the fridge venting off the side of the trailer, I hope that'll help. But I really think the outside temps will affect your fridge.
In the end, I'm hoping the cooler temps while camping at a higher elevation will keep it cold.
The name's Jeff
2005 Fun Finder T139FK
2008 Jeep Wrangler JKU