I drive one of those panel vans that has no rear/side windows, and, as much as I rely on my backup camera to... you know... back up, and, as much as I would give hard currency to have my backup camera 'always on' (especially as, in the T350, it displays on the rearview mirror - which is exceptionally convenient), Cromath is right that the angle is all wrong for proper perspective for driving - it will get you in trouble because the camera's focus is on what is immediately behind you (in both the Ody, and the Transit), by two car lengths things are getting fuzzy, and by 4 you can barely tell what is displayed... That misperception is going to get you in real trouble real fast...
If your rear view mirror is completely blocked by a ceiling mounted 20" display (*facepalm*), as cromath suggests, get a driving camera with two pickups, there are numerous units that have a builtin forward facing and a remote (for rear or any other direction) camera, and put the display in front of your (now useless *rolling eyes*) rear view mirror. That's going to vastly outperform the backup camera, and be cheaper.