Adam, I tackle this issue by gluing the front strip to the carcass (long grain
to long grain so movement in its length is not an issue) then gluing the side
strips only on the front 3-4 inches. Use a fine finishing nail on the back end
of the side strips. That keeps the front mitre joint closed but allows movement
to the rear.

Cheers,
John Johnston

“There is a fine line between hobby and mental illness.”