because ours was in very bad shape i bought one for under the bed between the rails, just behind the pass side w/ the filler in front of the fender. there is room below the bed and above the frame rail. it fits well but takes some work to do. i was re-doing lots of other welding and engine fitting, and a new axle, so this was a logical re-do and i could provide the needed room. some install the tank where the spare tire fits. I'm running a 6 cyl so the exh system runs down one side and the tank is on the left. i installed a 2000's type chevy cable crank- up/ down system for my spare tire. life will be better when we get older and have to change the tire... cause i ain't laying on my back to fetch the heavy tire by lowering that long bar down.
do a search for under bed gas tanks.

http://www.stovebolt.com/bboard/cgi-bin//ultimatebb.cgi?ubb=get_topic;f=22;t=003566#000000

pros:
it's out of the cab and safer under the bed between the rails. allows for more storage behind the seat.
you may also think about storage by
cutting the front sheet metal area under the seat frame to gain access under the seat.
cons:
it's a lot of work to make the change
but if the tank is bad and you have to buy a new one .... that may be the time to make the change
it's ALL up to you and the $$$$. you will have to close up the old hole and re-paint.

Jim & Caroline
The highway is for gamblers, better use your good sense."
Gooday-that's my 1¢ answer due to the lousy economy ~ cause I ain't got - no . mo . doe
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