I would just pull that thin skin off and skin it with a thicker ply. The ply on the sides and back will brace it plenty. Lots of people makes stands from 2x4 with no ply and vice versa ply with no 2x4. With both you’ll have no worries.
Both ideas given above will work. You can add the bracing or replace the panels without draining the tank, but using thicker panels in place of those thin sheets (which would be my preference) will be difficult on the back side since the stand is against the wall (plus you would need to move the desk or whatever is next to the tank).
