Many containers available.. Flowerpots should be UV stablized so if those 20gallon things were designed for plants, putting them in the sun should not be a problem. If they are the things I am thinking of with the rope handles and are simply a utility container. They will not handle the sun and will get brittle eventually. Whisky barrels would look nice ;> I still think though without rain and a bunch of big plants they will need watering more than once a week. Maybe one of those kiddie pools?? It would be big enough that it should go a week if you topped it up all the way with water (I think).
On the subject of wintering outdoors in a container above ground. Don't do it. The plants are highly unlikely to survive even if you piled the mulch on. IMO