With propane fridge the roof vent serves 2 purposes: fumes exhaust and heat venting.
With compressor fridge you still want the heat to escape, but I would seal one of these vents permanently.
It is supposed to exchange the heat with inside room air, but trailer is not a shore home, it can get darn hot in summer and you don't want more heat. For this reason, I would leave at least one vent open in summer. In winter I would seal both vents. If you're on grid and running A/C - seal both vents.