Re: Flush mount Rod holders !
I put two flush-mount rod holders on both sides of the gunwale at the stern on my '96 Targa 17 SC. Aluminum is pretty thick on my boat's gunwale (I'll gauge it and post thickness...bought the boat used and don't know exactly what the thickness is).
My intention was to use these for mini-down riggers, and they seem to hold up fine to that stress. I figured, "strong enough for cleats, strong enough for mini-downriggers." However, I wish I just stuck with the usual side-mount rod holders, I've got 10 more of those mounted to the inside of the gunwale, and they work great. You have to drill some big holes for the flush mounts (watch out for cables!), they have little "caps" that will probably need occassional replacement, and I bet for 99.9% of the applications a side-mounted rod holder will work fine.
Also, uninformed helpers mistake the caps on the flushmounts as "Gas Caps!".