Here's the Air Flo template I got from tracing the "real" thing.  This is the XL size, here
are the dimensions. 

(1)  16 1/2"  top of wing
(2)  19 1/4"  bottom of wing
(3)  12 1/2"  top of middle area
(4)    8 1/2"  bottom of middle area
(5)   13"       top of lower wing
(6)  11 1/4"  bottom of lower wing
       5"        width of each wing
      21 1/2"  length

I know it's not the prettiest, but it's the best I could do with what I have :).

Make marks on each wing.  1 1/2" from the edge on the
 front wings. On the back wings make a mark 2 1/2" at
 the top and 3 1/2 at the bottom of the wing. These marks are  where the elastic starts and where you will
 put the facing for your snaps.

Cut a piece of Ultrex for the facing as demonstrated here

Start the elastic close to the edge of the facing tacking it down with backward and  forward stitches, sewing the
 facing on at the same time. Continue to sew the elastic
 pulling it ever so slightly.  Ultrex gathers really well so if you pull too hard your legs will  be too tight.

When you get to the next facing, stop pulling the elastic and tack the elastic onto the  facing with a few forward
 and backward stitches

Here's the cover with the elastic and the facings sewn on

For the binding on this cover I use "100% Nylon Tricot Stabilized Interfacing" It is found  at Hancock Fabrics in
 the Interfacing bin. If you want a softer binding you can use  regular Nylon Tricot, however it is almost impossible
 to work with. I get 3 yards of fabric and cut it into 2"
 strips. 3 yards seems to be the prefect amount for an XL
 cover. 

Start your binding on a corner of one of the wings.  You
 can cut the binding in 1" strips and leave a raw edge, but
 I prefer to cut 2" strips and fold the edges in. It looks
 neater.

This really isn't hard to do.  As you sew, you have to stop
 a lot to keep the binding  folded and the cover in the
 middle of the folds.  This  is why the stabilized tricot is
 better than the stretchy slippery stuff.

When you get to the corners, lift the foot and pivot the
 cover.  You will have a fold in the  binding. 

Make sure you pull the elastic straight while you sew the binding on.  

When you get to the end, snip the beginning tail close to the edge.   

Continue to sew the binding on sewing over the beginning binding leaving a tail of about
an inch 

Fold the tail to the inside of the cover.   

And sew it down following the same stitching line on the binding. Cut the excess tail close to the stitches. 

Here's the leg hole with the binding sewn on. 

Place 4 stud snaps in each corner of the wings on the front of the cover  

On the back wings, place 2 socket snaps at the waist and 3 socket snaps at the legs.

The finished Air Flo copy!