Years ago we took our medium sized (35lb) dog in a Yak (single wheel) trailer. We had him on a short leash so he could sit but couldn't jump out. He never did seem to like it. Out on the trail we'd let him run along but he'd tire after a few miles so we put him back in the trailer. He still didn't like it. Had we done it since he was a puppy he likely would have been more accepting of it.