I used a 3/8" drive 12pt. 5/16 socket, 8mm will work also, but I find the 5/16 to be more snug. You may want to use an extension to clear the lip depending on the depth of your lip. The inner nuts, I believe are either 10mm (M7) or 12mm (M8).
I also used penetrating oil on the inner nuts to help disassemble the hardware. I found it easier to unscrew the 5/16 bolt from the nut, but you may try either way and see which works best for you. A helping hand is always nice, be sure not to strip the 5/16 bolt, they are $4.00/ea from Work's website. The 10mm/12mm nuts are cheaper and conveniently replaceable via local hardware store.
To reassemble, get a star pattern going on the first ~12 bolts, then continue clockwise, use blue Loctite on each hardware (a drop or two). Torque down to 15 ft lbs for M7 hardware. 17-18 ft lbs for M8 hardware.
Sounds like all you'll be working on are the rivets, but if for some reason you break the silicone seal, you will want to use some black RTV silicone, you can find this in most hardware stores. Good luck!