When it comes to trimmed surfaces I typically go to mesh and break the usual rec grid as opposed to trimming panels. Of course the edge condition isn’t smooth but I prefers full panels. So something even like quad remesh and then treating each quad face as a panel.
We could make an entire encyclopedia of the many ways to finish at a trimmed edge. Here is just 6.
But that’s the thing many new gh users don’t get. If the thing you are doing doesn’t have 1 obvious solution then likely a single component (in this case the lunchbox one) won’t do the job. There are too many possible solutions and no way to factually say one is correct, and when that happens, you need to be a designer rather than a slider mover 
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I wouldn’t mind these constant trimmed / untrimmed questions if they were always accompanied by sketch of how they expect the panels to end, atleast then we would know some thought is put into it and also we know how to help. I just wonder what did they expect the the grid to do?