Could put up ads in your local feed suppliers/pet shops asking if anyone's got any old horse trailers. Some of the old wooden ones weigh a ton & folks are buying the newer, lighter metal ones. Also they rot - unsafe for moving horses, but safe enough for housing goats, with a little ingenious patching-up. The top-half of the back can be blocked-off easily enough with a peice of ply to provide more shelter, but you can just park them with their backs away from the prevailing wind.
Easy to move around the field too
- just block the wheels when you park them up