We based our design on a model promoted by Nature's Harmony Farm. The idea was to keep the bottom open so the rabbits could graze on grass but make the structural parts that touched the ground wide to discourage the rabbits from digging out. After raising rabbits back at our Shoreline house in suspended wire cages, I was keen on doing something different that could give them more space and allow them to forage for more of their food. Still, I was a bit leery of the design, and even phoned into the the Nature's Harmony podcast to ask about problems they experienced with rabbit escapes and rabbits getting soggy in our wet winters. Although they've taken their podcast section down, they assured me that escapes were not a serious problem if the shelters were moved frequently and that the rabbits wouldn't get soggy if they had a raised covered area. Lesson learned: I need to trust my instincts, because the rabbits preferred to sit on the grass even in the rain and got very soggy in the winter, at times so bad that I needed to bring them into the garage to let them dry off. And second: I had lots upon lots of escapes. I lost one doe to a predator after she escaped during the winter. A replacement buck we got early in 2012 confounded all our attempts to make a maximum security rabbitat, and he spent more time outside the shelter than in it. The last straw was found when all the young rabbits (did you know they are called kits?) escaped not once, but twice in the space of a week. Trying to catch up 8 super speedy tiny rabbits is no fun. The problem is not that the rabbits are tunneling out, but rather that they can squeeze through the tiniest gaps between the base of the rabbitat and the ground. Our ground is very uneven, so attempting to get a 8' by 4' wooden surface to lay flat against the ground was next to impossible. We tried plugging the gaps with stray boards, but they inevitably would still escape.
Some farms use shelters with slatted bottoms to keep the rabbits from escaping, but this significantly reduces their ability to graze, and would need to be very close together to keep in tiny 3 week old rabbits.
I haven't completely given up on rabbits, though. While I don't want to put them back in small suspended wire cages, I do want to put them in a protected, secure area. Thus, I've decided to try raising rabbits in a colony style in the brooder stall we used to raise the turkeys. In this setup, the buck, doe, and young rabbits all live together. They have lots of space and deep bedding to absorb their manure. Every day, I bring them fresh grass harvested with a small push lawn mower with a bag attachment.