The best way to haul an Amphi is always a topic of discussion among Amphicar owners. This is due to the fact that the bottom of the car is flat like a boat - no frame to throw a chain around.
What I use is a 16' X 6' Utility trailer with duel axels and duel brakes. The trailer has an oak floor, so I've bolted two wheel chocks in a position so that I can drive Amphi right up the ramp and against the chocks. This serves two functions. One, it locates me in the same spot each time. And two, it keeps the car from moving forward during transit. Next, I took U-bolts and positioned them directly in front of, and behind, all four wheels. I drilled the holes in the floor slightly oversized to allow for the bolts to drop down flush so that I can drive over them, and then pull them up (about 3/4") to hook the nylon tie-down staps to. These staps are over all four wheels like a sling. I bought mine from JC Whitney - Part Number 12ND8169A with my own ratchets. Finally, I hook one chain from the tow hook forward, and one chain up and over one of the propeller shafts. These too, are hooked to U-bolts positioned in the perfect spot on the floor. Neither chain is ratcheted down tight, but the perfect length - they're just there for emergency.
Amphi rides great, and he loves it on his own trailer! I feel confident that no straps will wear during the trip because the nylon is touching nothing but the rubber tires - no fraying on metal. Loading or unloading takes less than 5 minutes.