On my Alaska trip I was planning to take some very remote roads and I wanted to be able to carry more fuel than the stock 29 gallon tank. Sounds easy right? just drop a 100 gallon tank in the bed, well I am planning on sleeping in the bed with a topper and the thought of sleeping on top of a 100 gallons of gas isn't too appealing. I did some research and ended up ordering a 55 gallon tank from Aero Tanks. If I did this again I would go with the 46 gal tank from Transfer Flow.  
  Instillation was not as easy as I had hoped I had to drill 10 holes in my frame (not really a problem but not easy either) the first time I put the tank in place I needed some spacers totaling almost 1" to get the fit right. The hardest part was the 2 holes I drilled in the Cross member under the bed. I needed to drop bolts down through the holes but there is no way to get in behind to guide the bolts through the holes, finally my friend John who owns a machine shop came up with the simplest idea. use very fine wire and feed it up through the holes and then wrap it in to the threads of the bolt and pull them down. After 3 hours of swearing at the bolts I was done in 5 min.  
  The major elements of this install were.
  1. Dropping the old tank and skid plate
  2. Removing the plastic wheel well liner and filler neck from the drivers side rear wheel well
  3. Drilling 10 holes in the mounting flanges of the tank and the trucks frame.
  4. Swapping the old fuel pump and pickup in to the new tank.
  5. Installing a new vapor recovery valve on the new tank and some minor reworking of the vent hoses.
  6. Cutting down the old filler end filler vent hoses
  7. Bolting the new tank in place
  8. Passing out from sticker shock at my first $100+ fill up. But now I can go 600+ miles on a fill up.
  
  Things I didn't like about this tank and Install.
  1. For almost $900 the fit and finish were really poor but it has never leaked
  2. The fuel pump mounting in the tank is kind of cheap, I suspect my errant fuel gauge readings that developed during the trip is because the pump assembly is moving in the tank.
  3. The new tank reduced my ground clearance by over 5"
  4. Having to put 1" of spacers on the rear outside mounting point.
  5. Losing the skid plate but my friend John helped me remake the old one to fit.
  

The New Tank Just out of the Box

Close ups of the top of the tank

The next 3 shots are of the new and old tanks side by side

Fitting the new tank

Look at the gaps!

The Impossible under bed cross member. I almost just welded the tab to the cross rail.

Next I sprayed lost of black paint and undercoating on the tank to seal and help protect it from the gravel roads of the north

I also modified my old skid plate to cover the front part of the new tank.