Think it would be alright to use that inverted dado, or rabit joint, but in the upper piece only do 1 cut, leaves a little more meat on the board and 1 less cut to do.Like This:
__________________________
|xxxxx
|xxxxxx____
|xxxxxe|ooo|
|_____|ooo|________________
|ooooooooo|
|ooooooooo|
|ooooooooo|
|ooooooooo|
Also, with those screws from the inside, would you reccomend screwing them while the glue was drying or afterward?