On 9/2/2015 9:51 AM, Oren wrote:
On Tue, 01 Sep 2015 19:37:31 -0700, Don Y

The problem lies in the fact that the door is a sealed unit. E.g., you
could mount it "inside out" and not notice any difference (except for
the stiffeners). There is no way to peer into the doors construction
to identify how much reinforcement is within and where, exactly, it
is located.

So, it's like trying to fasten something significant to an interior
(i.e. hollow!) household door -- with the exception that you *know*
the interior door is SOLID at the top/bottom/left/right edges!
(hence, a safe bet for the hinges and door knob hardware!)

Given what you stated, carriage bolts through the door may be the
solution. Use a lock washer under the bolt nut. Perhaps paint the
heads to match the exterior before they are installed.

That;s what I've been hoping to *avoid*! : E.g., at the very least,
putting just two bolts on each hinge (hoping the remaining sheet metal
screw can continue to serve in its current capacity) means 10 visible
"dots" on an otherwise *smooth* door exterior.

Replacing *all* of the screws (for hinges and stiffeners) would
pepper the exterior of the door with 100 of these! :-/