I don't see any issue using zip bases on the bottom of your panels. But I also don't see a point in doing that. Normally tying cables under the panel is not an issue. The cables running between panels, and over to whatever pass-thru path you used, is where you need them secured. That's where wind, and maybe even your feet, might move them around. That's where just a dab of Dicor or short strip of Eternabond tape is quick and easy. Just every couple of feet is all you need. And it isn't an issue to slice through if you ever want to reconfigure the array or replace a panel, connector, etc. And you would not want to use those zip bases out on the interconnecting cables where UV would destroy them very quickly.