I would be looking for an alternate way to carry those bikes. If you get a lightweight bike, as already mentioned it is going to be fairly expensive. I would NOT want to put an expensive bike on the rear of the trailer for several reasons.
1. Too much bouncing goes on back there and it is too hard on the bikes and the carriers.
2. Too much dirt and dust back there.
3. Too much chance of them getting hit by a following vehicle.
4. Too much chance of the bumper or hitch failing from the bouncing of the bikes.
I would find a way to carry them in or on the truck or trailer - anyplace other than the rear of the trailer.
Barney