Old Fridge vents for air conditioner?

Seems like it would be better to draw the intake air from the roof vent, and route the exhaust through the wall vent. I'm thinking there would surely be moisture in the exhaust, if you run that straight up you might end up with condensation running back down into places you wouldn't want it to go. I'm planning to put a portable AC in the closet above where the fridge went - am putting in an ice box - and will run the vent out the side fridge vent. My trailer didn't have a roof vent for the AC, just two side vents. I figure it can draw enough air from the closet space (and there are closet vent holes). Not ready to install it yet, but I'll post photos when it's done.

That is what I was thinking but I didn't consider condensation issues. An insulated duct up might help avoid the condensation problem.

Any ideas on how to modify the vent to prevent birds from roosting in it. Don't want bird poo down the back of an air conditioner. I'm not really happy about the amount I currently have to clean up and don't want any more!  My vent:

Just re-read the first post, and realized you're going to put an electric fridge in under the AC, is that correct (at first I thought you weren't putting any fridge in)? I'm not sure how much cooling air a compact compressor fridge needs compared to an AC, but it needs some, and the heat extracted from inside the fridge has to be vented just as the AC heat does.

Built-in, under-counter fridges apparently vent out their fronts because of the lack of airflow inside a counter, is that the type you are putting in? If so, then the old vents can be used solely for the AC, while the fridge vents into the camper. But if it's a regular, free-standing type like a dorm fridge, then the airflow has to be inside the cabinet along with the AC airflow. And if the AC is hogging the old vents all to itself, then you would be in effect "building in" a fridge that is meant to be free-standing, which will overheat the fridge and/or kill its efficiency.

I don't know off the top of my head how to calculate the amount of cooling air the two new appliances will need in comparison to the old propane fridge, you'd need to assess the venting requirements of both, and make sure there was enough airflow for both. Perhaps finding out how many cubic feet per minute of air each appliance's exhaust fan moves would help give you the answer. But I suspect the roof vent isn't large enough to exhaust enough air for both without some help, like more fans (a row of computer fans in the upper vent, maybe?). You might have to seal off the fridge from the AC entirely, and build into-the-camper cabinet vents for the fridge, to replicate the airflow the fridge would have if it was standing in a room. Some tricky duct work, sounds like.

You don't want the AC to intake heated exhaust from the fridge to cool itself either, as that would kill the AC's efficiency. 

Interesting engineering problem.

Birds? Just add some stiff screens in the vent.