I have been seeing two different sized tanks in the 4500/5500's 44 US Gal and 53 US gal. The 53 gal is of coarse longer has anyone had what kind of troubles with moving it forward or leaving it where it is distance wise from the rear axle? I am thinking that it will have to be moved further forward to get under a pickup box ??? The rear fuel tank is where I would like to put the spare tire? I was looking at one of the 7500's and it has side mounted 63 US gal fuel tanks with associated plumbing it probably goes with the reg factory fuel system that the trucks have? But they suposedly needs the 22.5 tires on it?? A gent in town has a pickup Kenworth and he has smaller saddle tanks that look like they would fit? I didn't look what capacity they were? Plumbing wise might be some work to do? Where there is a will there is away! And I will have my way! I hope?/ Maybe?:D