When I swapped to an under bed tank my truck was being built as a long distance daily driver, so I wanted all the fuel capacity available without hanging down too low. Rock Valley built a custom tank to my specifications for $550, back in 1998. I’m not sure what the same tank would cost today.
The only mistake I made was mounting a tight elbow on top of the tank to connect the fuel fill. The elbow caused fuel to kick back and shut off the nozzle. Filling the tank took forever, so modifications were in order. Details can be seen on posts #11 and #22 of the following link:
http://67-72chevytrucks.com/vboard/showthread.php?t=444502Post #50 shows the aircraft cap that replaced the fender/neck fill.
Here’s what the tank looks like from the rear. Despite the capacity, it really does tuck up nice and tight:
[IMG]http://img13.imageshack.us/img13/8337/post003m.jpg[/IMG]