I am just getting into frame assembly, and before I even start I want to be sure that I should draw my wireframe as if SW will extrude material around it on center? In other words, as if the wire frame were piercing the center of a center rectangle. Thanks.
I'm sure you must be using weldment to do the extrudes (profiles along the path), this will set the profile centered on the path. Just to add that you can position the profile using locate profile option in the weldment.