That's exactly what I am going to do,I am going to use a hinged screen door on 1 side and buy a window screen like I have on my house that is 3x5 and have that below the window AC.
I guess I will make some type of insulation plug that will go in the door and window for the summer and take it out in the fall and spring so I can use the open screened area.
I bought the screen that hangs and covers the rear but it is flimsy and a pain to keep it closed and sealed at the bottom,I am sure a moveable wall will look and work better.
I am going to make wood frame box to hold my gas cans when I am traveling that is 5ft wide and the right width to keep the cans secure and the right height so when I take the cans out I can put the box under the rear ramp so I would have that space like a deck,and maybe put a tarp top over the ramp.?
I am going to hinge the wall to the frame on the bed shown,and when it's open it will cover the bed and when its closed it will fit flush with the wall on the other side.
I read that the 6500 btu they sell at lowes for 160.00 is quiet has a remote control and will cool 250 square feet so I think that should work great.