"Ken Moiarty" wrote in message

How about making and attaching a bracket of some kind to the bottom of
the unit, shaped such that it will fit into the 'groove' of the window
frame, thus providing locking support at the base of the unit? And if so,
are there no such items (or kits) on the market ready made for use in
slider/casement windows for just this purpose? And how might I achieve
the same at the top of the unit (where it will meet the plyboard)?


I don't know of any kits to do that. You can probably put a piece of angle
iron or perhaps a 1 x 3 across the top as a stop held by the bracket on the
AC.