Sliding dovetails to fasten a table top

I frequently find myself lying in bed half awake at 5AM and to amuse myself, I start running through my current project and what I would like to happen that day.  Of course, I never get the amount of work done that I think I will, and it sometimes goes in a completely different direction than what I've thought out, but it does give a chance to do some creative thinking.  I've built a number of tables, recently, and they present challenges that are their own.  A solid wood table top 3 feet wide will move almost 1/2 " seasonally.  Holding it down flat and fastening it to the legs while accomodating this movement is always a challenge.  I started building the top around a sliding dovetail to do this job.  The dovetailed rail gets screwed down to the legs, then the top gets slid onto the rail and glued together.  With the dovetail slot cut 1/2" longer than the rail, there is plenty of room for movement and the dovetail holds the top flat.