You first have to find out if it is legal to pull two ball hitch trailers. Some places allow a ball hitch to be pulled by a fifth wheel.
Next you do not want to pull from the prop guard. It's no where near strong enough. You would have to attach to the main frame members and then figure out how to get it off so you could unload the boat.
Of course, if you could back that rig up you would get into Ripley's Believe It or Not.