I keep breeder boxes on my rimless tanks...however mine are all custom made 3/16 glass, so may be stronger than normal rimless ones.
I usually just adjust the foot things so that the box is level, however I lost a couple of the foot things and had to compromise....I used an empty small water bottle and squished it between the box and the glass tank and it stays perfect there...you can adjust it to fit so that the box stays level.
(In a pinch we all have to work out something fast even though its not very pretty looking
These are heavy duty acrylic and are made to hold just enough water to not break them or have them crack. I have been using mine now for about a year on and off and no problems (other than losing/misplacing the equipment for them)
I usually keep mine bare with just leaves (oak/ial) and some moss and an airstone inside, however when I set it up for the Taiwan females to hatch their babies in, I used some of the soil from their own tank to line the bottom...that works well however babies crawl into the soil and dissappear (hard to find them until they grow bigger, then they can't hide so much)
I currently use them to house my CPO's that I have for breeding, put one in each side until they grow, then they get the whole box to themselves.
good job I only have 8 of them or Id have no where to hang any more boxes.