I got one of those fancy-schmancy Ramcharger fuel tanks.
On the stock truck there is a crossmember that goes between the rear leaf spring mounts; that crossmember needs to be removed. You also need to remove a support brace that runs parallel to the frame and that connects to that crossmember. And you need to flatten a sheet-metal brace that's built into the bottom of the bed.
Then you need to bolt in the two crossmembers from the RamCharger; one goes in front of the tank, and one goes behind it. Depending on your hitch mount, the rear crossmember might interfere with things, or you might not need it.
Then you can use the straps that came with the RamCharger, but they won't fit too well. The tank mounts in our trucks at something of a funny angle, so the staps need to be lengthened through the use of a drop-down hook. Or you can fabricate new straps.
Considering that my drop down hooks popped out when I got rear-ended by a Corolla and then I drug my fuel tank across 400 feet of 91 Freeway, it might be a good idea to fabricate custom straps or to use safety chains just in case.
I cut out the Ramcharger's fuel door and welded it into the side of my bed for the stock appearance. To make room for the filler neck, you need to cut a couple slots in the bottom of the bed and weld a second bulge into the inside of the bed.
You also can use the heat shield from the RamCharger that goes in between the exhaust and the tank. Unless you have stacks or something.
The sender that comes with the RamCharger works on a slightly different ohm range than the one that comes with the truck, but it can still be hooked up on a switch so that you can read both tanks. When the R/C tank is full my truck's fuel gauge reads 1/8 tank before full, and when it's empty it reads 1/8 tank before empty.
Also, the tank's filler neck is smaller than the Diesel neck; you need to find a Diesel filler neck or else the Diesel pump won't fit. And the stock vents in the R/C tank are a bit too small for high rate Diesel pumps, so you can't go full flow with the big rig nozzles.
And the fuel lines in the sender are a bit smaller than what comes from the Diesel.
Actually, I would suggest finding a sender out of a Diesel vehicle, but I don't know if it'd fit in the tank. And if you were really concerned about it, it'd be cheaper to put a few lines through the tank with bulkhead fittings. Altough bulkhead fittings can also be expensive.
Total price for me was about $250 for the tank, crossmembers, fuel door, bulge, filler neck, heat shield and straps, then $500 for the welder guy to put in the fuel door, $50 for the 6-way fuel switch, and probably another $50 for the bolts and other little stuff I'm forgetting.