Some are
Some C22 trailers are double axles and they can certainly be added to a single axle trailer if one wishes. The concern is weight, weight distribution and dimension. If the bigger C25 boat is too far back on the trailer, it will become back heavy and too light on the tongue while possibly adding stress to the trailer frame. The bunks dimensions height of the keel and such are also important. Another concern is the vehicle weight limits,. engine power and towing capacity. For us the C25 would put us into a totally dfferent weight class for the vehicle.