I dont think there is a right answer for tank placement to be honest. Youre carrying 10-30 gallons of highly volatile fluid and some other not so nice stuff with ya no matter where it is on the truck.

On the other stuff, youre welcome. It really does help to write the stuff (goals/end state) for the truck down. Besides, if ya keep the truck long enough, youll get to build it a couple times and maybe a couple different ways!