I have a 14' raft and I haul it on an 8' fold up trailer, no problem. The tounge is barely long enough, but it is, even on tight turns. The bed itself is almost exactly the same size as the flat part of the raft bottom, the front and rear curve up of course, so they would "hang off" regardless of the length of the trailer bed.
Depending on the trailer and towing vehicle, be wary of how long you extend the tongue and how you load the trailer if you do. Extending the tounge can shift the weight forward of the trailer axle, depending on how you load it. And that in turn will put more tongue weight on the rear of the vehicle. So you have to be wary of the allowable tongue weight on your vehicle. You can always load the heavy stuff (cooler full of beer) in the back for towing sto compensate though.