I can't take credit for either of these things but I will pass on what I have learned.
We have a 2019 MHC 330RL with a Dometic RM1350 13.5 cu ft four door fridge. We have found it works well but can get a bit warm in the fridge in the afternoons-like many others have found.
I read a post on the Montana/Montana HC FB page about this fan assembly for the Dometic fridge and it has great reviews.
https://www.ebay.com/itm/Dometic-Ref...-/181208057633
It's not expensive so we gave it a try. Easy install as well. The fridge cooled down much quicker than usual with the fan running. Today the fridge has held 35 degrees all day and in direct sunlight. We do not have slide toppers either. The temps have been around 80 here today. VERY pleased with the fan. The air moving inside the fridge is very noticeable and we have no other fans in it the fridge-as a test.
Part two of getting better performance from the Dometic fridge comes from what time of day you turn it on. I read on a SOB forum about the periodic defrost cycle of the Dometic fridges so I looked in my owner's manual and found the same info.
The Dometic RM1350 will go into a scheduled defrost cycle 60 hours after it is turned on. The defrost cycle takes 120 minutes. After that, it will perform a defrost every 48 hours. Knowing this, the manual recommends turning the fridge on between 4pm and 10pm. I turned the fridge on at 1pm yesterday so that the defrost cycle will happen at night when it's coolest instead of in the afternoon or during the day when it will be warmest or when the doors are getting opened often. We do not full time. We are going on a weekend trip and getting the camper packed. We brought the camper home from the storage place, set it up and then turned on the fridge on electric.
Also here is a helpful video with some other fridge maintenance tips that may help all fridges with better performance.
https://changinglanesrv.com/rv-maint...refrigeration/
These things may not help in all situations but they are worth a try. Good luck.