Kyler mentions he used a Trek Transit Deluxe bicycle trailer because it was lightweight, could be taken apart quickly and stowed in a small airplane. He was also interested in the Trek's stroller accessories such as the castering wheels and padded handle.
Add a carbon fiber plate to stiffen the floor.
Add castering wheels to make a stable four-wheeled cart that still turns like a two-wheeler.
Slip tubes into the square receivers already on the trailer.
Drill holes for lynch pins.
Add nylon webbing to the tube sides for tug lines.
Add a front tube between the two square tubes for the poles to pivot around.
Secure with cotter pins.
Bend the poles up so they're in the same plane as the dog's back. This keeps the dog's back legs from getting caught in the poles, the ends of the poles from poking the dog's eyes, and the tug lines above pee range.
To keep the poles in place underneath the trailer, push tee nuts through a rubber strap and thread them on the extra length on the wheel mount bolts.
Use the strap to fasten the stowed poles under the trailer.
Snap the push handle from the stroller kit into the round tubes at the top of the trailer. This handle prevents you from running into the trailer and you can use it to guide your dog or push the trailer through snow etc.
To make brakes, add pipe clamps to the poles and cover with clear tubing. The tubing protects your legs.