Yeah, I definitely spend more time working on her than getting out. But she's brought me back and forth across country many times, so I can't complain too much.
I didn't get to do too much with reinforcement. I tried adding more glass, but that didn't work out so great. I used the West System epoxy instead and ran a couple of layers over the interior of the fiberglass to add a little more stability and to waterproof. I just couldn't think of a good way to get more structure up there because the roof is pretty curved. I even looked into steaming the wood like they do for boats. Hadn't considered gardening hose.
To make mounting points for the headliner boards, I used West System with a filler added (silica) which thickens it up. I made it the consistency of peanut butter and adhered blocks of wood to it, then used sheetrock poles to apply pressure until dry. It's holding up well so far. You could do the same to bond your furring strips. They make an adhesive in a caulk tube as well. I have one but didn't use it because I was only using a little at a time and thought it would probably dry up between uses, but for a larger project it might be easier. The people at WS were really nice about questions too.