This is a 3-piece model, so take your time in removing each piece from the etched metal frame they come in. The best way to remove these is with a hard surface and a very sharp hobby knife blade (be careful!)

The first piece you will need is the middle, or "box" piece.

As you might have already noticed, this piece has a rectangle etched into the bottom of it. The first step is to fold each side down so that you create a box. The half-etched fold lines should be on the inside of the folds.

Next, position and glue the bottom piece (the one with rivets on it) directly on the cab of you model, being careful to not plug the long slots that the AC box piece (that you just folded) will fall into.

One the base is glued in place, you will need to mount the box piece on top of it using glue. Prior to gluing, make sure that all of your sides are at 90 degree angles from each other to ensure a proper fit in the base slots.

After your box is secured in place, you can attach the top piece of the AC unit with glue. The 5 holes in the box piece are there to allow room for the glue to form a stong bond.