I tried to load my mother's dog into my more or less stock (topless) kid's trailer. He didn't like it at all. I could barely convince him to get in if I held the tongue on the ground and very steady. As soon as I moved it, he was out again.

Of course, a kid's trailer design is a bit awkward for a large dog.

Anyway, hopefully your dog finds the trailer concept more enjoyable. Apparently lots of dogs do fine with the trailers.