I got the titan tank for allot less than 2k. I like the idea of just pushing a button and transferring fuel into the main tank while driving down the road.
Are you planning on posting any writeup and/or pictures for the install? I'd be interested in seeing how it sets up for the Ram and where you end up putting the fuel door.
Why not mount a fuel cell? They are safe, inexpensive, and come in a ton of sizes.
Still takes up space and you need to figure out a way to transfer the fuel. I get that some people are turned off by the prices of Titan Tanks' options, but they're one of the few players in this part of the market and I do believe they're the only ones who use high-grade plastic on their tanks (I get the steel vs. plastic debate, but I do see the plastic tanks lasting longer in northern regions). So, to some degree, Titan is able to get away with charging higher prices.
Also, I don't see any safety issue with mounting a fuel tank behind the axle in a diesel vehicle. Some of the OEM C&C trucks have fuel tanks there. With a gasoline vehicle, I'd have more concerns putting a fuel tank in that location. Diesel is a lot less volatile than gasoline.