Something that I do to allow different sized tubs in the same rack is to do multiple depths.

For instance I built hatchling/juvie racks with 12qts on the bottom and 6qt on the top. They are all the same width but the 6qt rack isn't as deep (15 inches I think instead of 18).

It's basically like building 2 racks and stacking them on top of one another using metal or wood dowls and holes to hold them together.

In your case you could do it with 3

Also something to consider is that with one thermostat and different kinds of heat tape you will have different heat results. 90 degrees on the 11 inch won't be 90 degrees on the 4 inch or 3 inch because they run at different wattages to attain certain temps.

I would suggest using 4 inch everywhere but running multiple rows of it on the 41 qt containers (3?)....and maybe 2 on the 32 if you want.

Hope that helps,