It's a weird art, decking. I see your point on end grain. If I went with no wide margin, I would have a narrow margin piece with a caulk joint between it and the butt joint. Take the modern boat above with no wood trim, it has a metal trim piece on the butt joints of the lockers. Do you think that is caulked?
In the end I think I'll need the trim or frame for hinging and other requirements I can't seem to do without using the trim. Trouble is to my eye, often the trim looks like too many pieces not making much sense. If you have any photos, please post. Thanks Westy.