If you don't have to run a bladder, you may want to consider a side tank on a 250. We ran them on our Hypers until the bladder rule. Found them to have more side bite, less tendancy to pull you around going into the corner, and less tendancy to loosen the car as fuel load burns off. An overall more balanced feel. This is because the fuel is centered in the chassis, instead of hanging behind your rear spring axis.

I have a right side tank (have 2 actually) you can have if you want it. Does not include cap, but does have 4 mounts. Fits Hyper, but could be used on other chassis with simple tabs added to the frame.