I built a trailer for hauling firewood and I guess it could be used to haul a moose.
Most home built ATV trailers are the same width as the quad, trails don't need to be widened then. I built mine wider, inside bed dimensions are 3'x8 and can carry almost as much as a short box truck', so that it would be less likely to tip over due too the high center of gravity and narrow stance. The axle was laying around at my in-law's house, from a Dodge car I believe because there was an axle for sale in the classifieds that looked the same, and I cut and welded it. I reinforced it with 1 1/2" pipe, fit right in the U channel, and that was to keep it straight as well. Ground clearance is excellent at 11" I believe, bike with got hung up long before the trailer will.
I am going to add a trailer jack and safety towing light kit so that I can haul the trailer out with the bike then hook up to the truck and drive it the 2 miles home.
We stopped dragging moose out (too hard on the machines and
what do you do when you came to a bog?)
I built a slide to haul wood in the winter, picture a wide toboggan with sides, used two sheets of plywood and an old truck bedliner, cheap and light. Acts like a trail groomer as well, smooths out the high places and fills the low spots. It way work for hauling across a bog once or twice, I will look for photos.