I have two portable jugs that I use. One is a 5 gallon round looking thing that has a nice spigot on the end. When boondocking we usually put this on a table outside and draw from it for coffee and drinking water. I also bring along a 6 gallon plastic jerry can looking tote that I lift up and empty into the trailer water tank.
You could put the barrel you describe in the bed of your truck and let gravity do the work. You could build a small platform to put under the water can if you needed more lift.
You could also get a 12 volt water pump to do the transfer if you had to. I have a friend that has installed two large tanks in the bed of his truck, one for fresh water and one for gray water. He has a pump that can pump the gray water into the aux tank and he lets gravity pull the fresh water to his trailer. A pretty neat system but it does add a lot of weight to his truck.