I have a few customers that use barrels, for me it's actually quite easy to fill as the chute is high enough on the back of the truck. Just tip it up and dump it in.
As far as getting to the bottom that could be a problem but you could flip it over on it's side once you get it half empty. They aren't hard to move, you just tilt them a little and roll it on the bottom edge to where you want.
The bag method sounds, expensive and like a lot or work.