I have not seen 6 and 41 in the same rack.

AP makes a rack that does 15 and 32qt in the same rack, as they are the same height and you can just fit two Sterlite 15s in the place of one 32..

You will run in to a lot of problems evenly heating and using the same thermostat on such a big disparity in size between a 6 and a 41.