Is it feasible to attach a glass storm "window" to a french door with
15 single pane, fixed lites? The door would be 6'8" tall by 5'4" wide.
 The glass could be framed with aluminum or plastic(?)like a large
storm window and would be attached by means of cleats on the bottom
and screw-on clips on the top and sides, similar to those which hold a 
mirror to a wall. To make the panel less fragile, two panels could be
used, each half the size of the doors' glass area with one placed above
the other.  Marvin makes a french door with 15 single pane fixed lites
with an indentation in the glass area to accept an "energy panel" made
of glass and aluminum or perhaps plastic which stays in place by means
of screw-on clips on all four sides.  These clips and the indentation
allow the panel to fit flush on the door.  However, the muntins don't
have a profile which I like and so I am hoping I can use a french door
which I like and attach a storm panel as I first described above. This
will make the door heavier and I plan to order a reinforced jamb,
heavy duty hinges and longer and heavier screws. Is this feasible?

What you didn't know about the Marvin door is that you can get the
muntins in virtually any style you desire.  Go to www.marvin.com and
use the dealer locator to find a dealer near you.  I'm guessing that
you want the energy panel in order to improve the energy efficiency of
the door.  It is already very efficient, but the EP will make it more
so.  I sell Marvin windows and doors in Indiana.  There are many, many
options, but a good representative at a Marvin dealer will be able to
help you find the right door.  Good luck!