These WILL corrode and fail anywhere the lines vibrate and abrade (line clips, against other wires and hoses, and anywhere gravel and debris can get to). Stainless steel lines will outlast the truck many times over. GM cannot get our dollars if parts last, so they will not use stainless. Only issue with stainless is must be tightened with more force if spliced, because the material is that much stronger.
GO STAINLESS! The additional cost is minimal to the ease of mind that your kids will not have a catastrophic brake failure. GM should be forced to recall their brake lines (Honda and others used the same defective steel lines, and stood up to their failure by issuing a recall and changing the source of those brake lines.