So I built a box to house a tool in my shop because why not practice dovetails. I made a simple lid from some flat sawn maple and I'm just thinking that it's certainly going to cup over time so I should take some precautions. Easy enough to do breadboards.

Two questions: given that this isn't a piano, would just domino'ing the breadboards to the end of the top be effective at maintaining flatness? Or is the integral tenon somehow more important thant I'm assuming? I figure its grains going different directions so they will resist cupping, but I'm not positive.

Second, the top is ~12" x 20". Is a 1 1/2 - 2" end sufficient? and if so, how long would you make the tongue? Is there some rule of thumb here?

I know that none of this is probably necessary, yes. Just a chance to do something different in the shop so why not!