That’s a possibility, glassing entire inside of the doors. I think Eric does not mean that though, he is saying to glue the bottom door stiffener into place before cutting the door free. You would have to sand-to-fit the stiffener without the door in hand though… might mean crawling in and out through the transom multiple times. Ugh.
Glassing the whole door inside might have other issues as well, particularly with regard to window frame fit.