Try cutting the trailer close to the tongue and then inserting a 3 foot section of square metal tubing that will fit snug but still slide freely into the end of it. Slide the tubing in or out until you are satisfied with the length. Then, drill a couple of holes into the side of the tongue all the way through and into the tubing inside and insert hitch pins to hold it in place. Then, loosen the bracket that holds the winch onto the trailer and slide the winch and bracket up towards the tongue and then winch the boat up until you get the proper support at the rear of the trailer.
And, voila, trailer extended without any welding! :wink:
Oh yeah, this wasn't my idea. I found it on the 'net.
Of course this will only work if you have enough room to slide the winch and bracket up towards the tongue. If not, I guess you could remove the winch and bracket and fasten it to the added tubing.