I had a Okanagan 96db , when I put solar on called them and they sent me a framing diagram , of coarse that was when they existed still.
The guys that owned the co and his brother are both at Adverturer now and , I hear rumors of them starting Okanagan up again once in awhile
You might call them and see if they have any info or drawings still.
Failing that , or maybe before that , I`d pull out the ducted AC registers , or speakers and look up in the ceiling , I believe its a wood truss frame ,with 3/8 on top and 1/4 on the inside or something like that, push up on the interior ceiling and see if you can tell where the framing is, its carpeted right? so you cant use a stud finder
Instead of using store bought Z brackets to mt the panels , use one foot long pieces of alum angle back to back to form a Z , that way you have more chance to cross a truss at a perpendicular angle , if you cant find the truss use a 1/32 drill bit under where the angle will lay to find the truss , lay dicor under the angle to cover the small holes and seal the whole thing down when you screw it down .
The other good thing about back to back angle is you can bolt them together , and un bolt them leaving the half that's mounted to the roof , and remove the panel if you have to later
