In addition to obtaining an owner's manual for the chassis itself, as NMRver suggests, you may also want to obtain one pertaining to the house portion.
Many RV manufacturers don't put out an actual owner's manual that is specific to the model. Many manufacturers provide a generic manual that covers all their models. Forest River, for example, provides a manual that covers all their motorized products ...or did through about 2009 or so. I'm not sure if they still do that or not. For example, CLICK HERE
for a PDF of the manual they provided during the time period up to about 2009 or so. This owner's manual may help you somewhat as it should cover a lot of things in their 1998 models too. Again, it's just a general manual that explains the systems that are common to most motorhomes and some of the specific items that may be related only to Forest River.
In addition to a generic manual, many RV manufacturers will provide separate manuals from the manufacturer for each appliance and other components which are used on the RV. Perhaps the former owner left them in a bag or box somewhere in the motorhome?
I believe, and Forest River owners please correct me, that the Windsong was discontinued in 2004 or 2005.
Also, you may want to browse or re-post your question and future questions in the Forest River Owner's Forum section of iRV2. Click here
to go to that page.