To expand on what the others have said, the roll servo goes on the spar (typically right wing, I believe), and the servo installation kit will come with its own bracket that replaces the lower W-823PP bellcrank bracket with an equivalent part that also holds on to your servo. Then, there's another little bracket that you include in one of the upper two bolts that comes down to help support the servo too. So, just keep in mind you'll be removing and replacing some of those bolts that go through the spar into the wing tie-down bracket.
The servo installation bracket is similar between all servo brands, but Garmin says that theirs is required for their GSA-28 servos due to minor clearance differences between theirs and others.
As for bottom skins, my .02 would be to leave them off as long as possible, because it will be a lot easier to run wires and rig everything with the skins off. And, you might find doing a thousand rivets on the bottom skins to be a refreshing change after being buried in fiberglass when that time comes... at least that's what we're looking forward to!

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Mike Jimenez & Sarah Hammonds
EAA Chapter 33 Prez & Soc Chair
Marion, IA USA
RV-10 In progress! (N165MJ reserved)
-Emp & Wings complete
-Panel wired up, working on Fuse & Finish
-Blog horribly outdated (sorry)
-Too many distractions, we will finish the plane someday!!!
http://mikeandsarahrv10.blogspot.com/
http://www.eaa33.org/