John
I have made these window/doors before. They are actually a very good way to go. Get a window from All-Rite
http://www.all-rite.com/ (verticle slider.) There custom made so you can get any size you want. Mount a Heavy Duty aluminum piano hinge (alum to alum, don't mix metals) to one side of the window. Theres your door. Using the door as a pattern cut the door opening 1/4" larger (all around) than the inside mounting flange. You will have to cut a slot into the mounting flange on the door to accept a strike/keeper opposit the hinge side.
http://www.rvlifestyles.net/Parts.aspx? ... 2003730023
for a "T" handel (avail at home depot) MOUNTED ON THE BODY___NOT THE DOOR. Put some kind of weather strip around the outside of the door and your done. The only draw back to this kind of door is that the slider is at the bottom. And your bedding will cut a lot of the airflow. Mounting the door slightly higher will help...but not to high. To high could have you singing Soprano...trust me, I know.
Happy Trails
Len