We recently created this under seat metal gas tank to be shaped and formed just like GM made them. Correct for 1/2, 3/4 and larger Chevy and GM trucks 42" X 18" X 8" and holds 18 gallon. Overall length 57 1/4". SURPRISE: Because the add spout is 15 1/4 " long, we can often add small parts in the box cavity at no extra freight cost. This long spout can increase UPS freight from $ 70.00 to $170.00. SAFETY FIRST,GM had the RIGHT IDEA! GM protected this tank by surrounding it with a heavy steel seat riser plus a double layered cab exterior. Certainly equal or better in safety than hanging it with little protection behind the rear axle! REMEMBER: the rear end Ford Pinto explosion in 1972 that killed three passengers? Check Google and type: 1972 Ford Pinto gas tank explosion.