Dave:
Back when I had more "disposable" income, I had Dee Zee custom build me a refueling tank out of diamond plate aluminum with a matching toolbox. Then I took a tonneau cover and had it cut down to fit the bed with the tank and toolbox installed. The tonneau is rolled up in the garage. Most of the time, the camper is in the bed and if the camper is out, the tank and box is in and the goose neck hitch is being used.
My tank is 100 gallons. I have a 12 volt tuthill transfer pump and a 5 micron in line filter. I put an RV style 7 way plug on the cord and I plug it into the male in the bed. I used to carry on-road diesel up north but now I just use the tank during farm time with off-road diesel that I pump from the bulk tank.
If I remember correctly, the tank and box was about $900.00. It's is really sharp looking. Right now, it's sitting next to the shop!!
You want to buy it???