I would not swap the short fence for a long one if I were you. The fence is short for a reason! A short fence helps to prevent kickback by giving the wood somewhere to go it it bends as it is cut. A long fence just forces the wood into the blade, making kickback more likely. Also, if it locks onto the back rail as well as the front, although it might be more sturdy it is less likely to be square.
You can make a new fence which is rock solid for not much money and I have published details of such a fence I built for my saw. It's rock solid and locks only at the front, on a 3-point saddle so it is always 100% square. I made mine, including new rails for the saw, for less than £50, IIRC, and most of that went on the clamp itself.
S