[JRTJH]

The refrigerator vent stack is specifically designed and sized to provide adequate ventilation for the heat produced by the refrigerator. There is "precious little overbuild" in that area due to the management of space requirements for any RV. Adding an additional "ventilation blocking structure" inside that "already barely adequate ventilation space" could, in many areas, cause the refrigerator vent stack to not remove sufficient heat and cause the refrigerator to perform poorly or possibly even damage the refrigerator cooling mechanism. Additionally, you'd be providing an open, direct route for carbon monoxide and exhaust gasses from the refrigerator burner to flow into the RV interior cabin.

The sidewall of your trailer is 2" thick. Why vent 4' away when you're only 2" from a suitable locationl

I wouldn't do it.