Here's the link to Firestone's air spring guide:
http://firestoneip.com/-/media/www/f...tcat_smweb.pdf
I Think you need a W01-358-6905 (page 104), which is a convoluted style air bag.
You should be able to read the model number of the air bag on the side of the air bag itself. It's a little difficult to see when the air bag is on the coach and depends on the orientation of the bag itself. The reversible sleeve air bags can rotate 360 degrees on the mount so it could be facing any direction.