Thomas, I just ran a test with your Box7.tcw in TCad v15 Pro, and the heavier line weight looks good. I went to Isometric_SE, selected all, set Pen Width to .02 in, rendered in Hidden Line. Created a new View comprising what was shown on the screen. Printed to CutePDF Writer, specifying the Current View to be printed. Opened the resulting .pdf in Adobe Reader and printed it to my HP Officejet Pro 8600. Line weights are nice and heavy. Repeated that procedure with all Pen Widths set to zero. When printed out, the lines are all thin -- substantially different from before, and not nearly as easy to see on the printed page.
Bottom line: It oughta work.