The fresh air intake on a window shaker is on the from intake side. Window shaker draw in air for the compressor from the top and sides of the case, then forced out the back.
Personally this is what I would do.
Using 1/2 or 3/4" plywood or is that's been treated/ painted. Build an enclosure about 2' past the end of the unit on 4 aides (top, bottom, left and right). For the back, I would panel that off, then using either a 6 or 8" hole saw, make a hole dead center for the exhaust to escape. The constriction should keep heat him, but not overwork the compressor.
Now for the intake area that the unit draws in to cool the compressor.
Use 2x3 and frame around the unit. Use the 2x3 the tall way to gain an extra .5". Use the same.1/2" plywood and make a case around the unit. There should be a 3" gap from.the window unit case and the new enclosure. Make this the same.length as the exhaust box you made. Your essentially making a box in a box.
The back of the unit should look like this. See drawing below. Im.trying to type this the best I can. It's easier to show that to type. As I don't think I'm getting my thoughts out as I like.
Pic 1 should how the exhaust port would be made.
Pic 2 (drawing) shows how you would build another box to allow air to come in for the compressor. This would start where my 2x4 support are on the opposite side of the exhaust box. And go as far as the length of the exhaut5box you made. You would need to use a 80j elbow and direct the exhaust down
