Just give yourself plenty of time, and a dry place to do it, ideally a garage or a marquee over you
I'd start on a friday evening, so if you run into any problems, you have sat to go and get tools/parts easily.
http://www.350z-uk.com/topic/94723-rocker-cover-grommets-no-need-to-replace-entire-rc/
You could just try the sealant down the sides first of all, run it for a couple of weeks, check the plugs and see what's happening.
Ensure you have something like carb cleaner to hand.