what I use is a separation container that hangs over the edge of the aquarium. its a completely sealed unit. which in the case of breeder boxes they have holes in the bottom or cuts and that will actually cause you to lose some if not all the eggs due to them being so small. ill post a pic. don't mind the guppies in their trying to get them to give birth XD.
the only time I use a breeders pen is for my live bearers. I used a net with my mosquito fish the firs time and it was a hassel and some of the fry got stuck and died so all my containers and pins are hard since there is nothing for them to get stuck in. with this container you will have to do 50% water changes 2 times a day and have an airstone. this is to keep fresh water in it and to keep things cleaned and once you have little fry you need to separate them cause if you put food in there with the eggs your once possible fertile eggs can get fungus which that can spread to the whole batch overnight. so you need at least 2 of these or even take a plastic tuber ware and poke small holes in it about mid way all around just one row and don't use the lid since they breath air. and place an air stone in it. what you want to feed them is brine shrimp, tubifix worms, flack food, algae wafers, and sera micron(fry food) this is all ground up into fine bits. trust me I tried live brine shrimp and the ended up getting bloated due to not being able to separate the eggs and shrimp well. and the reason why all this is so when you ready to sell them if you do they can be feed a good variety. also has high protein. when I make a batch I usually have 1 dried tubifix cube, 1 dried brine shrimp cube, 1 pinch of flakes, 2 algae wafers and a good sprinkle of the fry food. if you need any advice I think I still have a page on fry up. just check it out through my home page and then threads or message me XD. whish you best of luck.