The boat is 9 feet long and weighs over 100 lbs by itself (and the trailer of steel pipe is not exactly light weigh). You can see in the video it maneuvers nicely, and is not a problem to tow (though I wouldn't want to take it up any steep hills!)
Step 1: Trailer
Step 2: Gimble Joint
Note: the center joints are "loose fit" (not fully tightened). This allows the for the 6 degrees of freedom required for the joint to rotate along the X,Y,Z axis.
(Darn Rust - it has held up well over the last 5 years since it was built considering I didn't paint it)
Step 3: Wheels
Pneumatic wheelbarrow wheels provide the suspension to absorb road bumps and at bike speeds there is no worry about burning out the bearings.
The axle is a 3/8" steel rod with holes drilled in the ends for cotter pins (with washer) to hold the wheels on.
There is a reducer pipe fitting on the inboard side of the wheels to reduce the diameter of the 1" pipe to provide a better fit for the 3/8" axle.
Note: a joining fitting is required at the center of the frame to tie the two side of the trailer frames together.
Step 4: Roller
Urethane roller used on big boat trailers. I got this one at a sporting goods store.
Step 5: Connection
The connection to the bike is made by partially unthreading the fore/aft connector pipe. As it is being unthreaded from the trailer side make sure it is being threaded into the top elbow on the bike.
Step 6: More Photos
My two tow vehicles side by side.