In order to ensure that the flat head bolts in the top sheet would sit perfectly straight and flush, I drilled slightly over-size through holes in the top u-channel so a hex nut could go onto the ends of the bolts. But those nuts were now in the way of the sliding bar used to latch the side panels. A fix for that was to mill-out those areas from underneath the sliding bar (via my handheld router).
The mill marks were quickly removed with some hand filing.
To prevent the sliding bar from falling out of the u-channel, some small pieces of aluminum angle were cut and attached to the channel.
But now the angles interfered with the latching hooks on the side panel, so those areas also had to be milled away (via a center-cutting mill on the drill press).
Finally, one leg of the angle that was used to make the latching hooks was visible through the side panel perforated aluminum, so that too required having to remove around 1/4-inch of material (via my trusty router).