As already stated in other words, you need to...
1. Provide a way for fresh outside air to get to the vents on the side of your AC unit (intake air for the condenser coils)
2. Provide a pathway for hot air coming off the back of the unit to get out of the camper.
I simply put vents in my galley to let fresh air in, and build a box on the back of my unit that channels hot exhaust air to a marine vent on the side of my TD.
If you look at the photo below, you can see the the box for the back of the AC unit. On the side of the TD, you can see a tall vent with louvers, which allows fresh air into the galley area where the AC unit is. Behind that, you see a rounded vent that covers a four inch hole where exhaust air leaves the galley.
Both vents have bug screens to keep the critters out.
CD