First: you need to make a frame mounted on the face of the inside alum frame inside your existing door but make the wooden frame just about 1" smaller then the existing door opening all the way around except the floor of course.
Two.: Then make a wooden door much like the old country wooden doors found on farm houses. I built mine with a slide in the center to be able to open the main door hatch. I use Pexi Glass for the slides. I didn't glue mine together for fear of the glue coming apart in moisture areas such as early morning dew as well as when it rains. I screwed it together. Also I used the door support brace which at times needs tightened so the door doesn't sag. I have used it for two years now.
The second shot is the added screen on the back door so if I am camping near a lake i could see the lake or what not in the morning without getting out of bed. Yes the door goes all the way to the floor so critters don't get in.

