I use the rigid plastic holders.. they are stackable..
only you have to cut the two outside rows of cups off to keep the upper tray from binding on the incubator sides when the turner tilts..
you have to make sure you put the stacking posts front to back and cut off the cups on left and right..
however, I do not think this will work in a 1202 model with the hatching tray in the bottom the turners are too close together.
by doing this you essentially have two incubators' worth of eggs in one encubator,, just for the cost of 6 extra trays..