if the door manufacturers would make their doors properly
in the first place, there would be no need for the
"jamb sills".

Agreed. I tried to find a one piece threshold that wrapped up the sides of
the door frame. Or, a "one piece" frame like vinyl windows have. But, I
couldn't find anything at any price. Every door frame seems to be made the
same way, with the same vulnerability to wicking and rot.

The composite frame and sill liner combination seemed to be the best
alternative approach (if you don't want a storm door on the outside).

Anthony Watson
Mountain Software
www.mountain-software.com/about.htm