I have a couple of melamine racks that I use for smaller species.
I too am a big believe in the value of ventilation so I melt as many holes in my tubs as I think they can stand structurally.
Rather than use pegboard on the back of my rack, I leave the back open. I nail a short strip of wood along the top rear of each shelf which stops the tubs from sliding back too far. I just used cheap $0.39 yardsticks from Lowes for my backstops. They are nailed to the back of each shelf (including the top) and hang over about half an inch, which is enough to stop the tubs from going too far back.