Here is the situation...

I have a 2015 F350 KR, long bed, 4x4. At minimum I make a round trip journey of 752 miles once per week (376 miles each way). Sometimes twice a week. Plus another 100 miles of driving at destination. Lets call it 850 miles. Half of the time I'm towing at 10 mpg = 85 gallons. Add in an extra 5 gallons of emergency fuel as a safety buffer for idling in the extreme winter cold, making a minimum fuel total of 90 gallons.

My first thought was a Titan tank, but that would only net me 65 gallons. Not enough. Sure, I could fuel back up at my destination but diesel is, on average, 0.50 cents a gallon more than at my "home base." Right now it's about 0.70 cents a gallon more. Besides Titan tanks are very expensive.

So my next thought was an RDS aluminum tank mounted in my truck bed. I need as much space as possible so I was considering their 73200 model tank which is 60" long, 14" wide, and 26" tall. Advertised as a 90 gallon capacity but if it's anything like my other 45 gallon RDS tank, the "actual capacity" will likely be around 80 gallons. 80 gallons plus my factory 37 gallon tank = more than enough!

Here are my challenges:

1. I have an ARE truck topper installed to keep my cargo dry. It's a must have, and has solid aluminum sides. How could I fill the RDS tank? With it being mounted in the front of the bed I don't think the fuel pump hose would be long enough for me to crawl in with. Plus doing that would be awkward and potentially risk me spilling diesel over expensive cargo. So I'm thinking the best way would be to cut a fuel door in through the side of the ARE topper and install fuel hose from it to the tank. Not really sure where one could find a fuel door designed to mount on the side of a thin aluminum canopy wall

2. Plumbing the RDS tank into my factory tank. Best location to tie in?

3. Fuel transferring - gravity fed is not an option (do not trust it) so I would be mounting a pump inside the truck bed near the fuel tank. Mounting it inside the truck bed will keep it out of the elements and hopefully make it more reliable. I'd like to wire the pump up to one of my upfitters and have it tied into a 12v shut off solenoid to physically close the fuel line when the pump is not powered. Suggestions on a pump that is reliable in sub zero temperatures?

4. Overfill prevention. What kind of safety net can I put in place to ensure I don't accidentally forget to turn off the pump, overfill my stock tank, spill 20 gallons of diesel on the ground and then have the EPA called on me because Prius drove by and saw?

5. Lastly I will need a way to monitor the remaining fuel level in the RDS tank. I'd prefer not to mount another gauge on my dash. Mostly because there are not many good places and it will look out of place. Before anyone mentions the cubby hole long side the center console- this space is already allocated towards handgun storage.


The tank itself will cost me about $650-700 shipped to Alaska. My project budget is around $1200, leaving me $500ish for the rest of the stuff I'll need.

My typical MPG average between oil changes (5000 miles) is 13.1 MPG.

Figuring I fill up with fuel that costs $0.50 more a gallon 1/2 of the time right now, by my math, I the tank will have paid for itself in fuel savings in 21 trips... about 4 months. So it seems like a pretty decent investment and the tank itself will still have value after it's removed from the truck before I trade it in when the 2018s come out.

 

Why no gravity flow?


I love my setup with my gravity flow. I have a manual valve and a automatic off/on valve wired up to my switches. When driving I flip my switch and starts filling up my tank.


I did once thought of getting a diaphragm pump (1.2 GPM) and installing it to the RDS gravity flow kit with the overflow preventer. With a set of relays once the pressure gets to a set point shuts off the pump and triggers a relay and cuts all power to pump until the unit gets reset.

 

A marine remote fill kit installing the fill cap on the outside of the topper.

And gravity feed is the easiest method that you don't have to worry about over filling the main tank. There are a lot of people using gravity feed including myself.

 

I had an RDS in the shell of my 02. I just filled it by crawling in with the hose and never had an issue.



I used the RDS install kit from Northern Tool.

RDS Diesel Install Kit for Auxiliary Diesel Fuel Tank — Fits 1999–Current Ford, 2011–Current Chevrolet and GMC, and Dodge 1999–2012, Model# 011025 | Auxiliary, Transfer Skid Tank Accessories| Northern Tool + Equipment

I used this fuel pump/filter to transfer the fuel.



I basically tried to keep it as simple as possible.

 

Transfer flo makes a nice tank for your cover. However it's a bit smallish.

It's interesting that transfer flo is absolutely against gravity flow.