Can you recommend a seriously good marine-grade sealer? My roof is leaking in 3 places

(where the roof rack bolts attach, drivers side front and rear, and passengers side rear). I only want to deal with this once. I'm going to take the Rola basket and roof bars off this week and seal the crap out of all 4 side rail attachments, and I want to use something good, something foolproof. Something marine-grade so it never leaks again. If I flip the KK over in a lake, I want it to float! So what is the best stuff out there for sealing metal, but that still remains slightly flexible under stress (like when there is a load of camping gear on the roof) and can survive freeze-thaw in winter?
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2008 Liberty Sport 4x4 Automatic
Jeepin By Al 4" Lift Kit
BFG KO2’s 245/75R16
Full MOPAR skid plates
Rock Lizard Skink Super Sliders
AtTheHelm Front Recovery System & Roof RackM116A3 Trailer build thread: viewtopic.php?f=72&t=77997