I lashed a 2' square chunk of 3/4" plywood with a 3" exhaust clamp's U-bolt to the tongue and some wood screws to the decking, so I could do this:
Two 12As, one 3N71 transmission, a complete RX-7 front suspension minus strut housings (note strategic blocks of wood to keep it from sliding down), and the Contico box has another 3N71 and was packed to the top with starters, brackets, manifolds, bits, bobs, and other stuff.
The car also had a pair of transmissions, and the strut housings/brakes/rotors that went with the subframe, and basically was full from the bumper to the front seats. And also the passenger footwell was full of stuff.
Rear suspension (Mitsu Mirage-spec KYB AGXs, Volvo V40 "heavy duty" springs) is on the bumpstops. Trailer has more suspension travel because it doesn't HAVE bump stops.
Funny event: Was messing with the instrument panel data center when I hit a yumpy bridge gap. Backing up a bit: Unloaded, I can juuust make out the trailer box in the mirror through the slit between the rear wing and decklid. Fully overloaded like this, the entirety of the trailer box's lid was visible above the wing. Back to present. I'm flipping the dahs display from instant MPG to outside temperature or something, and I hit a WHUMP. Back of the car bounces up (no suspension travel, you see) and I feel a backwards jolt. In that moment, I take my eyes off the dashboard and up to the rearview mirror, just in time to see the trailer bounce up and completely fill the rear window. Then the trailer SLAMS back down (you think?) which kicks the back of the car up again, this time with a sideways element, and did I mention that we're on a narrow bridge in heavy traffic and we're going 75?
The whole rig settled down pretty quickly, and as a bonus, the tractor-trailer driver who had been tailgating me slowed down and changed lanes I didn't see anything falling off so I kept on going.
At the next fuel stop, I noted that one of the main ratchet straps had tore halfway through, so I supplemented it with another one. And now I have a bit more negative camber on the right trailer axle. Trailer tongue attachment points, though? Still solid.