Re: Trailer Conversion to a Pontoon Boat
Not very practical... There are two types of pontoon trailers, either a scissor type trailer which supports the deck, but also has a very narrow wheelbase, or bunk trailer which supports the tubes, but also has very small tires and an axle/spring design to keep the height as low as possible.
Obviously a scissor trailer is out, but with enough welding and metal stock, you could turn it into a bunk trailer. You would also need a new axle, tires, suspension, and also extend the tongue. A trailer meant for a 19 foot boat is going to be too short for a 21 pontoon. You need extra clearance on the front since you have two tubes sticking out on each side, vs a bow in the center. (or you just are VERY careful when you turn, unless you will have a tube in the back of your truck)
Long story short, you would be far better to sell your trailer and buy a pontoon trailer.