OK - I have made a breadboard end with a sliding dovetail for my latest
project. The width is 15". 5" of the top thickness is cherry, 10" of the top
is "Lacewood". The breadboard end is cherry. All QS.

OK - My sliding dovetail is not perfect. I end up with them too tight or too
loose. If too tight they will blow out the edge of the slot or telegraph a
ridge through the surface. If too loose then you have a gap. OK, so my
closest, when it slides together w/o too much pressure, yet will not fall
off easily, my middle ground, still leaves a small gap between the
breadboard end at the rest of the top.

I can pull this gap closed with clamps.

I know that your breadboard end should only be attached in the middle or at
one end.

If I glue the thing across the whole length and clamp it shut will I have
issues with wood movement given my description above? Doweling it at both
ends would seem to be the same as gluing the while length. One dowel in
middle probably wont close the gap entirely. Maybe just "a couple of brads
to hold it while the glue dries"? he he

Or, just tell me I need to perfect my sliding dovetail technique!

That "dowelling of both ends" idea can work. Just need a little
elongation of the hole(s) in the middle and one end of the panel,
preferably the one you won't see as much... Tom

Make your dovetail a little too tight and then fine tune it with a
chisel and scraper. You'll spend more time trying to "fix" it than you
would to do it right in the first place.