I have a two axle trailer with a 12' bed and I find it just about perfect for hauling the Zuki's around on. Any shorter and you run the risk of not having enough angle on your tie downs to secure the vehicle. You can reduce the size needed by using the tie downs that go over your tires though, a friend hauls his Samurai on a 10' deck using this method.
If you are going to tow a vehicle, I would make sure you have trailer brakes. It is just silly to haul that much of a load without the extra control brakes give you. Especially when you are coming down a hill.