Sorry to add to an old thread but it seems to me the major cause of the resistor pack blowing is because the blower motor is not blowing as well as it should.
The way it seems to be designed (with the resistor pack buried in such a stupid place) is so the airflow from the fan cools the resistor pack and stops it overheating. If the fan is failing (and especially if there are any rumbling or squeaking sounds), the airflow will be less than it should and it won't cool the resistor pack - especially on '1' when the air flow is minimal but the voltage drop across the resistor is at maximum. So it would be worth lubing the blower motor bearings if your resistor pack blows. Might save you replacing it again in a couple of weeks!