A housing structure for a vehicle electronic control unit (“ECU”) includes an ECU case, a mounting bracket, and a seal ring. The ECU case is for housing a vehicle ECU and includes a ventilation opening. The mounting bracket connects with the ECU case and is configured to connect with an associated vehicle frame for mounting the ECU case to the associated vehicle frame. The seal ring surrounds the ventilation opening and seals against both the ECU case and the mounting bracket. A method for mounting an electronic control unit (“ECU”) case to a vehicle frame is also disclosed.