Originally Posted by Spiffy Gem
That's because the frame of the oldies are not made to handle the weight and torque of a grey water tank. Light weight and no grey tank or heavy with grey tank. Pick one - unless very customised, you don't get both.
The original frame is fine for a grey water tank that is mounted immediatley behind the rearmost axle, or behind a single axle. A capacity of 25gal is ok, and will fit between the frame rails without modifying the cross members. Been there, done that. Worked great. One shoudl never drive far with a full grey tank anyways.