Hello Mel and welcome,
On the first question, I have not been able to find any site, free or
otherwise, that have information specific to the make and model of
older coaches, besides the odd manual on the oven or air conditioner.
Even if you did have the information, it would be impossible to trace
the interior utilities of electrical, water and sewer, as these are
routed slightly different on each vehicle.
You may wish to try RV Salvage yards to see if any salvage RV's still
have documentation inside. Here is the link to these sites
http://rvbasics.com/techtips/oldparts.html
On the second question, there is no way to cure the dual pane window.
The window is manufactured with a gas that is sealed in between the
two panes for insulation and UV protection. When the seal fails, the
gas escapes and the leak allows atmosphere into the opening and
moisture builds up a "foggy" residue.
The only fix is to replace the windows, and this can be done at any
competent glass shop or of course the manufacture.
Enjoy your new RV,
See you on the road,
Sam