We have a 2002 Montana that we bought in July of 2001. While our sofa is in excellent shape, it was time to replace the deteriorating 'decking' which is the fabric that the mattress rests upon.
Found and ordered ($169.95) our replacement decking from:
http://www.furniturepartsonline.com/...pair-kits.html
While they don't have the speediest shipping, it was free and it did arrive 10 days after ordering.
If you need to go through this also, be sure to open up your sofa and look for a manufacturing tag on the metal bed frame tubing from probably 'Leggett & Platt' or 'Hickory Springs'. You'll need to know the model number and manufacturer before you can order.
Not a very difficult installation, just tedious and you will need some arm strength. (Besides scissors, pliers, and a phillips screwdriver).