FMX---We would all like steel fenders on our rides. That being said, there is the cost factor to consider. Steel fenders cost about 3 to 5 times as much as fiberglass ones, if you can even find someone producing the fender you need in steel. If you have expectations of finishing and driving the car in this lifetime, then probably fiberglass is the way to go. You can always get the car up and driveable, then go to swap meets and look for original steel fenders. I have built cars with steel fenders and with fiberglass, and I find that fiberglass fenders are more user friendly to work with if you have to do any screwing around with them to fit the contours of your car exactly. Many people are running fiberglass fenders on 1928 thru 1936 cars, where there is a lot of unsupported fender hanging out in the wind, with no difficulties. On a car like your 48, the bulbous shape of the fender and the fact that they have a supporting flange all the way around will make them even stronger. The only thing I can say about glass fenders is that you should coat the inside surface with something like spray or brush on truckbox liner, to prevent stones from flying off the tires and causing "star-cracks" in the gel coat, which will show up in your paintjob. I am running a steel body and box on the roadster pickup, with fiberglass fenders, grillshell, hood, and splash aprons. Remeber---the car you are building is going to be a hot rod. Nobody will know that you are running glass fenders except you, and the touchy feely crowd at the car shows. In my opinion, running fiberglass fenders really has no down side, and its a heck of a lot cheaper.