Dave Riendeau said “I tried the stopped groove on another box I made, it is a pain to work with a plough plane. This is one area I’d like to see Paul address in the future. There has got to be a simple method for this, craftsman of old had a simple method to deal with this I am sure. Did they only groove two sides?”
Sometimes two sides and sometimes 4 depending on the how you were schooled or which you prefer. This is regardless of whether the corners are dovetail or comb joined.
Ploughing 2 sides leave you with one end to shorten and one groove to cut by hand, whilst ploughing four sides leaves you with a slight alteration to make to your dovetail layout, with a half lapped/mitred dovetail concealing the groove – avoiding the need to cut a stopped channel – and the open gable is already partially pre-cut to the correct height due to the presence of the groove.
Both of the above methods work and several others exist for joining precisely the same intersection. 😉
Over the years I’ve found a common flaw with such sliding lid designs is the liability for vestigial lipping to fracture or tear off if abused in some way. One means of reinforcing the grooved edge involves drilling for a gluing in a number of fine dowel pegs (Cocktail stick sized) which are then cut and finished flush with the surface.