Thought I'd weigh in on rearing methods with my limited but positive experience with rabbit tractors.
My friend and I decided when we moved "up North" this past summer to Ashland area in WI that we were going to raise rabbits for food, fur, and the learning process and found ourselves in the housing quandry also. I found some rabbit contacts in the area including an old friend who had been raising rabbits in a rabbit tractor with success. I ended up borrowing his tractor and eventually making a larger one to house more rabbits.
This tractor I designed has the cross section of a child's drawing of a house (think triangle on top of rectangle) and is about 8 feet long. One side is two plywood pieces (for wind/sun/rain screen depending on season) and the other is 3/8 inch hardware cloth. For the bottom I thought about slats but was worried about weasels entering under the gaps at each end. Consequently, I instead surrounded the whole perimeter of the floor with about 5 inches of hardware cloth and had overlapping 2x4 inch mesh wire which sits on the ground. This leaves a pasture of 7 feet by 3 feet for the mother and young housed therein. Hypothetically a weasel could burrow under the hardware cloth, but this hasn't happened yet...knock on wood. (our cats did kill a weasel near the rabbits though!) On one end we have a nest box measuring about 3x3 feet and a foot tall with a hinged door.
This setup has worked remarkably well for us with no sickness (since starting in July) or any adult mortality issues. Pasture was not lacking on a friend's hayfield site, so we moved them around multiple times/day chasing the best mix of grass, clovers, and other good forage. We also fed the rabbits any "weeds" pulled from the garden and fed them about a cup/day of our sunflower seed/bread crumb/oat groat mix that we make up. Our original doe Nightshade kindled first in early August after living in these environs for the second half of her gestation. Nightshade raised nine healthy babies (she killed #10-the runt of the litter) all survivors of which grew with vigor. These young have never eaten pellets and besides the daily protein sunflower mix get all of their calories and nutrients from forage and household vegetable scraps. We routinely give brambles, willow, dandelions, catnip, wild strawberry leaves, lambsquarter, velvet leaf and a ton of other weeds and edge browse plants in season. This setup worked quite well, but we were a bit too slow to move the adolescent gang away from their mother which we learned the hard way when they smothered her next litter
Despite this loss, all of the young grew to a decent butchering weight in about 20 weeks. I know that this is slower than a pellet-fed rabbit, but considering their food is largely free, they are consuming a large amount of healthful and medicinal plants, and their organs and internal health during butchering all showed perfect signs of health, I have no complaints thus far.
Now that it's winter, we have the tractor stationary with a tarp around it and about 18 inch deep snow piled over the whole structure but the plywood doors which we keep bundled with blankets. We've also added several inches of straw which we routinely add to and clean out about every three weeks. This winter arrangement has worked well for the surviving rabbits (now four does including Nightshade) though we now need to begin separating them as one of our young does just kindled for the first time (!) and she and her seven little ones need some privacy! Happy news, but we again have a need for additional housing which we will temporarily meet via an XL dog carrier.
Here are a list of my thoughts on the success we've had:
1) Nightshade is a silver fox and her babies are 1/2 sf, 1/4 new zealand, 1/4 flemish giant - Silver foxes are known for doing well on pasture
2) Nightshade, although previously eating a diet high in pellets and corn, was also tractored getting pasture as more of a supplement before
3) We weaned Nightshade off her pellets over the course of a week or two substituting larger and larger portions of sunflower seeds and breadcrumbs before removing pellets all together
4) I believe that all animals need great diversity in their diets for optimal health - pasturing the rabbits on an the old hayfield was the easy solution
5) Using a large mesh floor works well for the rabbits to harvest their own food and still keeps them from burrowing out
Here are some limitations our system has had so far by our reckoning:
1) The tractor took a bit of time and effort to make...we need more!
2) Despite being more room than the average hutch, we feel that these tractors are too small for very many adult rabbits and are ultimately better as maternity wards
3) Having only one nest box means that territorial disputes will enter into the box causing unnecessary stress for all the rabbits.
This upcoming spring, I hope that we will be able to make two or three more tractors each with two nest boxes attached. This would allow us to keep our four does - 2 each sharing a tractor, a buck, and young rabbits all with minimal competition. The buck will be alone only for short periods as he can cohabitate with the does well until they are ready to kindle. In this arrangement my hope is that we would also fence off a larger area to use for an exercise run that would have burrows, and interactive features for jumping, play, and exercise. Does anyone else have plans for a similar "playground"?