A commercial tank can hold more rock than you can get into it, without fear of the bottom not holding.
Now the stand????
Plastic rims get old and brittle. They develop small cracks that go unseen, until that day you notice a bow.
Pretty easily replaced, but one of those jobs where the set up/prep work is harder than the job.
People have done a number of workarounds with a homemade brace glued to the existing rim.
I don`t set my rockwork any closer to the glass than the easy use of my algae scraper allows.
Others have rock resting against the glass with no problem.
All Malawi,All Mbuna,All Action,All the Time