If you can't find lecca, you can also 'suspend' you vivarium floor with a true false bottom. Get five or six 3" tubes, put a sheet of 'eggcrate' (the white grid found in office light fixtures) on top of the tubes, then put your screen on that. When you are finished you can cover it with soil or wood chips as a substrate.
This makes a hollow cavity to collect water in. You can make a kind of sewer 'manhole' on the surface with a hidden cap on it to siphon the water out when it gets too full.