aksail, what the heck is a 90 degree impact driver? does home depot sell 'em? I was going to try the perfectly fitting slot head with vice grip trick but thought I'd ask the forum first to see if there were any magic tricks.....
and freesail99 these bolts penetrate horizontally into, and terminate in, a little solid fiberglass wall that comes up from the deck and on which the cap rail sits, not vertically through the deck, which unfortunately means no luck on finding some nuts nicely exposed under the deck.
thanks to both of you.