Setting row-layout to a fixed width

I'm making a table with (non-editable) rows and columns. I'd like the 
columns of all the rows to line up and change to accommodate various 
length strings as they are added to the table.

Each row of the table is a row-layout which contains some row-layouts.
I thought I would do this by finding the minimum size of each column and 
then setting the interior row-layout widths to that value.  But I don't 
see a way to set the :visible-min-width of a row-layout programatically. 
I can work backwards to find ratios to use for the columns but that is 
awkward compared to setting the width directly.  Is there a way to set 
row widths to a value or is there a reason it doesn't make sense to want 
to do that?

Mitch