This is our third year of running these tractors, and I think I like this design (the third one so far) as pretty much our permanent design. Some day I'll get around to writing up a nicely detailed description of the construction process. Basics are that we have gone as lightweight as possible (I'm an average-sized fairly athletic woman, but I find the stouter designs really obnoxious to move daily) so most of the construction is 2x4s ripped lengthwise along with modular panels. Both the bottoms and tops are made from panels of "wire decking" made for pallet racks. You should be able to get a bunch of them for relatively cheap, used, from used manufacturing supply places in large-ish cities. We got around 2 dozen for like $15 each in Sacramento. We remove a fair number of the cross wires from the bottom pieces to reduce weight and increase gap spacing lengthwise, which helps the grass to be more available, but keep the lengthwise-running wires so that at least one dimension has around 2 inch spacing. Even then, on rare occasion if I've parked the tractors over a little furrow or hole, kits have escaped. The tops keep all of their wires, and are augmented with a layer of 1x1 wire to help keep raccoon arms from reaching in, and then covered with plastic feed sacks for shade and precip cover. The feed sacks don't last forever, but they are free and very lightweight.
They are divided down the center so each tractor provides two holes, plenty per side for a buck or doe with a young litter, or up to about 4 grow-outs. Dimensions of the wire decking are in the neighborhood of 4'x4', so that's the footprint. And we do 24" tall sides, all of 1/2" sturdy hardware cloth to prevent reach-ins by raccoons. One end is a mix of plywood or OSB and more feed sacks, to give the rabbits a more private retreat. And we install bunny buckets, and most recently, a nice shelf in that end, for additional shelter.
I am very careful scooting them in the morning, as I have caught one or two legs and it isn't pretty. The buns learn pretty quickly to surf along on top of the decking, jump in their buckets, or up on their shelves. I would never, ever keep a rabbit in a bottomless tractor. Although the worst diggers are does, especially when pregnant, even my bucks will occasionally get the urge to dig, and without a true bottom, they would be out of there. We have too many predators, and I consider my breeding stock to be too valuable, to have escapees wandering around the property. Knock on wood, so far nothing has managed to break into a tractor, although I have encountered the J-feeders ripped off in the mornings. I suspect they will hold up to all the medium-sized guys, and maybe coyotes, but I am sure a determined domestic dog (or a bear) would have no problem. Luckily our bears seem much more interested in our chicken feed and bird seed than the animals themselves.
As I said, I think I am fairly happy with this particular basic design. Whenever I get around to it, I'd like to upgrade the feed sacks to panels of Coroplast (the stuff political signs is printed on) so that those parts will last longer, but it's fairly low priority as I always have plenty of feed sacks around. I'm just a beginning woodworker, so my construction process is very inefficient and kludgey in some ways, but I haven't had to make very many of them so I can deal with that.
There should be a bunch more pictures on my website,
http://www.flyingfossilfarm.com .
