I've grown rhubarb in nursery containers. Your barrel planter would work well.
Rhubarb needs a good supply of nitrogen when it is growing. Top-dress with manure, if you have it, or you can use fertilizer, either a balanced NPK type, or one which supplies more N and K than P. When my rhubarb greens up in the spring (or just before I expect it to), I will spread a couple inches of compost over it, since I don't have a trustworthy source of manure nearby.