I agree the minimum size in a glass tank should be a 40 breeder. 30s don't have that much floor area. But instead of spending a bunch of money on a heavy glass tank that is still not really that large.. consider using a plastic storage tote. You can either cut out the lid and glue in screen, or use a hole saw and cut holes around the outside, then screen them (this method is better for high humidity animals).

I'm in the process of moving all my large frogs into these, They don't crack, they are lightweight to clean and move, super cheap, have more ground area, and stackable when not in use.

You can see one of my Smooth Sided toads sitting on a cork slab if you look close.