I bought a 60 gallon transfer tank & pump and put in the back of one of my M-1008s, one of the best purchases I ever made, no more plastic cans, except for the darn small engines & 2 cycle. I got a very nice one from Northern Tool that has a concealed pump and a nice tool box above the tank for around $1,600. It is all aluminum, DOT approved and US made. There are larger less expensive transfer tanks for less $ if light weight and the discrete pump are not desired.
My understanding of the DOT regulations is that you do not need a hazmat placard, and the hazmat endorsement on your CDL, if you use a DOT approved tank under 119 gallons, for diesel. I'm sure enforcement varies form place to place, but if a DOT officer finds someone driving around with a full 55 gallon drum, they will not say it is OK. If you have a CDL, they probably won't let you plead ignorance, not that that would necessarily help anyway. If one were to get in accident with a full, non DOT approved tank, they might be open for some pretty stiff fines.
That said, I'm sure a lot of people safely move full drums of diesel around all the time, and maybe should keep doing so, but it is good to be aware of the regulations.
Heating with oil, I always have around 200 gallons of dyed #2 I could use in my generators, but when I tried to get them to deliver on road fuel for the trucks, they said local regulations require me to get permits, inspections and a double lined tank for that (even when my 275 gallon heating oil is the same stuff), go figure.