If you want to add some life to those cages you could use some polyester auto-body filler to cover those corners. In fact you could trowel it on in a way to add a radius to all of the interior edges which would make things easier to clean. I'm 90% certain that polyester body filler with stick to melamine. Maybe rough it up with some sandpaper to be sure. Or try a test on the back of the cage.
Another product that sticks to melamine very well (forgot to mention this in an earlier thread) is Drylok Masonry Waterproofer (latex). It's a hydraulic cement based "paint" that has excellent adhesion to many surfaces and is water-proof. I know of one guy who tried to make an aquarium out of melamine, thinking that with the plastic layer it would be waterproof. Not surprisingly the tank started to leak within a day or two. He drained it and painted the entire inside with Drylok and it held water for well over a year after than until he sold it.
Drylok has a very rough surface and will not make for an easy to clean surface. Another contact of mine painted some cages with it and then siliconed scrap vinyl flooring to the bottom for an easy to clean surface. He also painted over the drylok with a high gloss bathroom paint to make the walls easier to scrub down.
-----
Currently keeping a small collection of various Gonyosoma. Both G. janseni and G. oxycephala.