RE: Insulated headliner
The beams run from side to side , the planking will go fore and aft.
As the PH was created from 2x10x10 , which are trimmed to about 6 inch depth to get roof camber , there is loads! of space for insulation. As we like cool places as much as FL , the whole depth will probably get rigid foam.
Wood or other trim will be required at penetrations , air cond , vents, opening hatch and the rest , but not to hold the planks in place.
To keep down the holes (and therefore rot starters ) for wiring and goodie mounting the plan is to epoxy the mounting lumber outside the GRP covering .
The PH top now extends fwd of the PH so a flag holder base will be installed between the forward opening windows.
This points down so the wiring will be protected , and will then lead up (with a drip loop) to the radar mounting base , which actually gets the VHF , steaming light , anchor light , search light and perhaps the "crew meals owner absent " light.
All will be below the dry exhaust height , so those 12ft bridges will still not slow us down.