I had one made up 750 long, 400 deep, 600 high, it has top bracing on both side with a lid front and back, this is all 8mm.
Nice and strong in case I knock it or drop a rock on it while cleaning the inside.
I cant think of anything worse than injury to anybody or the thought of comming home to dried up fish and a wet floor and the basment below all soggy.
For the few xtra bucks go solid.