Size for a weasal cubby box size?

Today i went out back behind my place on alford creek to see if their was any beaver, muskrat, or mink sign i found a set of weasal tracks. I know the main way of trapping them is to use chubby box with a #1 longspring, but i dont know how big to make the box. And since im only 15 and new to trapping i figured a weasal would be a little better trophy then the squirells.