10-column grid in t3-base template

Hi,

I'd like to use the t3-template as such: 5 column-layout: sb1-content-sb2

content consists of 3 columns (c1,c2,c3) so basically a 10 column-based grid...

all collumns should be same width (sb1=c1=c2=c3=sb2).

Max-templatewidth = variable, max:1240px;

I've tried to change the layout by changing less-file (with help of docs.) but backend keeps giving me 12-columns (instead of changed 10)

see attached design.

Is this possible with t3-fw and t3-template.

Thanks in advance

I do know the t3 (and other) frameworks are based on an even (12 cols.) grid but I really need an odd-grid layout with l-r sidebars same width as content-columns....

See attached design please

Mark