A coach builder's owner's manual is a bit slim on info if they can find one going back that far. Normally what you will find is general paraphrasing what the individual OEM manuals recommend and such. You friend would be better supported finding the individual manuals for the installed items such as the fridge, generator, chassis, awning, water heater, air conditioner and such. They still may have troubles considering the age of the coach but the general operation and recommended maintenance might still be applicable if they find something very close to the item model and year.