@Mech_Engineer: no problem! I appreciate the input. Many minds make light work :) Just found this forum and hope to stick around. I just googled "mechanical engineering forum" and was happy to find something for the question. Neat place.
@Mech_Engineer: I need the square tube outer profile to remain unchanged because something rides up and down on it with rollers. What you describe sounds like I'd need to clamp from outside the tubing?
I'd agree with these comments, especially xxChrisxx's that "CAD is CAD is CAD." For the most part, I'd agree. If you learn one, you'll get a vast majority of the concepts. Sketch -> feature -> repeat as needed -> make drawing.
My university used SolidWorks. My internship during college used...
I'm designing something in which an insert fits into a piece of steel square tubing. The insert is held in place by a set screw threaded in the insert, which is in turn loc-tited into an aluminum "plug" (wider surface area) and is clamped to the inner wall of the square tubing with a hex wrench...