RE: mounting dinghy to cabin top
I think a lot depends on the dinghy hull. If it is fiberglass and has some weight I would through-bolt. At the back a 40 foot trawler there isn't much movement while underway, but rolling forces would worry me. As Chip said you should use the same bedding techniques you would use for deck work. I recently noticed a couple of access panels on my cockpit ceiling to access the underside of the aft ends of the brackets I see none inside the salon which leads me to believe that they either used a toggle bolt or used a sounder and located solid wood.