Yep....a thin layer of RTV sealer.  I use the Suzuki stuff - but Hondabond, Yamabond, 3Bond are all acceptable.  I would stay away from the normal RTV at the auto stores - it seems to set up really quickly and doesn't give you time to work.  Only put a thin layer on - if you get it too thick it can plug up the oil passages and starve the cam for oil - and if the stuff squeezes out in big globs it can come loose and plug stuff up.

Look in the tech section for the proper torque of head cover screws...and easy does it as they are small land can easily strip out the soft aluminum cylinder threads.  Also make sure you put the sealing washers in the correct location.  And don't put sealer where the little oil reservoir for the cam lobes is.....there is nothing on the cap that pushes against that and the sealer will just be sitting up there waiting to come loose and clog things up.

And....don't do this!

Thanks Dave!  

And yeah, I know how much to NOT put on with sealer.  I was taught long ago that a solid thin coat with no gaps will go MUCH further than sealer applied too heavily.  I've seen the proof in both cases.