Thanks for the response. I have bins a little bigger, 12 quart. (shoe boxes for people with huge feet) I first had bought 6 quarts like you have, but I thought the sub would be a bit thick as a result because of the dimensions of it. I'm not sure, but I don't like that idea very much. I now have room for more substrate in there and still have room for the mushrooms to grow for the most part without going dub tub. If it is necessary I can go there in the last few days of fruiting.
I have decided not to mod anything to start out with, we'll see how that goes. I'll just flip the lids for fruiting stage: the lids are slightly concave when flipped, so on both sides the lid wount touch the bin. That sould provide plenty of air exchange. Seems to me to be a good idea to start out without mods for this, and see how that works out. As soon as it doesn't seem to work I can go and mod the empty bins/lids I have.