I use a folding wheeled trolley similar to the one that Barb in Louisiana posted, and made a bag for my machine. I use Velcro to hold it on to the trolley. What I like about this is that the larger wheels work well in gravel or over rough surfaces, and if it's rainy/snowy/muddy I can detach the wheeled part and put it on the floor while belting my machine into a seat.
I couldn't find a hard sided case at the time I needed a travel case so I made the bag. I needed 24 inches wide x 9 inches deep x 13 inches high. I still haven't found a rigid case the right dimensions.