You could use a metal garbage can or metal drum. Fill with 6 to 8 inches sand, use a tree stump or four 6"x6" timbers bolted together in the center. Timber length should be a comfortable working height for you, back fill with sand (great sound and vibration absorber). If you go with casters, use 5, not 4, to prevent it from tipping over and a couple layers of plywood between the casters and the can for better weight distribution. The metal can and sand would also be pretty fire safe, if you're forging metals. Great anvil by the way! Hope this helps.