Would it not make sense to go back to a set up that actually functioned then?
If the "new" system doesn't work, maybe its time to go back to the old proven effective system. Get the resister and pig tail from the older Dakota and adapt it to the modern version, then put it someplace where it can get some air flow, that new location doesn't even have to be in the heating system. It almost sounds to me that the "new" heater box has some poor air flow places and Dodge decided one of those places with poor air flow was a great location for the heater resister. Or they went too far on cutting the material list and have too small of connections/components for it to function properly, or both.

Giving this some more thought, I wonder how much effect the problems Dodge has with the blend door failures is effecting the resister's life span? Gene