solid bench seat joinery

I  am building a solid seat bench similar to the Thos. Moser English Bench (see the company website.)  I am looking for ideas on how to attach the solid wood seat.  I've thought of using sliding dovetails wiht the male portion of the dovetail cut on the top of the side rails, then gluing only about an inch of the dovetail to allow for wood movement.  My problem is that to do this right and to have it add to the integrity fo the bench, it has to be precise.  Not sure that my skills are up to that but I'll do it if it is the only way. 

I'd appreciate any thoughts you might have.