to try and limit the variables lets establish the requirements to be meet:

lightweight; just have to be strong enough not to flex with air traveling over and accomplish the remaining tasks.
still swing open like a conventional door, alternative hardware permitted; hinges and handle.
have ability to locate lexan in the up position and down position.

the project in question does not have a window frame; that would make attaching the window in the up position easier, in my opinion. so this leaves one with either making a frame and attaching to the door or making a metal frame the curvature of the natural glass and attaching the lexan to get the appropriate contour. this would then require a channel to allow the window to go up and down within the door.

i was planing on locating an aluminum frame around the top part of the door where the window will be move. this would add some strength and also allow me to weld a tab that i would attach a nylon buckle. this buckle would be routed up over the frame -> below the bottom of window -> back up inside of frame and over the top -> heading back down the edge that would normal mount the door panel. this would allow a means to slide the window up and lock it.
here is a image borrowed from another site to better illustrate this.


are there more efficient ways of accomplishing this function?

how have people accomplished this feat in the past or plan on doing so?

 

lol ... you can make a custom braket for bolt it from bottom of the window were it usualy goes bolted to the top part of the door which you do not cut