I have installed several prehung exterior steel entry doors over the
last few years, and virtually all of them have minor leaks somewhere
around the bottom. The first was the entry door to our garage, which
has now rotted and will need replacing this summer. Obviously, I don't
want any other doors to rot like the first one, or worse yet cause
structural damage to the buildings.

The problem isn't the door; it is drainage around it.
It is obviously sitting in a puddle at times.

Three doors leak, none of which are anywhere close to the ground.

1. Garage entry door. Top is protected by a 12" roof overhang with a full
gutter system. Bottom of door sill sits about 4" higher than the concrete
walk in front of it.

2. Back door of house. Gable roof end only overhangs about 6" and is
approximately 12' above the door. The sill of the door is roughly three
feet off the ground with a wood landing about 6" below the door.

3. Front door at in-laws. Hip roof overhangs about 18", but no gutters
installed. Door sill is roughly three feet off the ground with a wood
landing about 6" below the door.

In all cases, the only source of water would be windblown rain, or
splashback from the deck/patio below the door. The doors can't be raised
any higher and still comply with stair height codes.

Anthony