MISF & I built one. I set the tongue length to be a little longer than 1/3 of the total distance from the ball to the axle. Trailer tows so well that you wouldn't know it's back there except for the weight. Has been stability tested to over 80 mph (friend borrowed it for a run to the desert), reported no sway or other instability.
Donor was an IH 3/4t pick-up. Bed was really rusty. Located a less rusty GM bed and then the IH bed had a Sawzall Accident. Then we were given a CUCV bed so the first GM bed also had a Sawzall Accident.
Used an old square spline - cone washer Dana 60 axle for it's wheel hubs and stub spindles. Inserted the stubs into a piece of tube MISF had left over from Demo Derby car. Axle holds about 3 gallons of gear lube, but the bearings will never get hot.
With the leaf springs used on pick-ups shocks are a must.
In the first pic you can see the "kickstand". Knowing that this trailer would get borrowed (part of building it's intent) we first used a kickstand rather than a jack so as to hopefully minimize potential damage. In the same line of thinking there is a 7 pin trailer electrical socket in the side of the tongue. Each different type of tow rig socket has it's own jumper. If a jumper that fits the borrowee's tow rig isn't in the tongue box, then the cost of borrowing the trailer is to build such a jumper. Anyone who cuts an existing jumper no longer can borrow it.
The trailer now carries it's own spare in the section behind the axle under the bed. It is held up by an S-10 spare tire winch, which is driven by a chrome lug nut of the same size as those on the axle's hubs.
1st pic is tongue detail
2nd pic is frame less bed
3rd is first GM bed shortly before the Accident.
