The easiest way to add wheels is to find some casters that will handle the weight, you can get these at Northern Tool, Harbor Freight, or maybe even Tractor Supply Store. Then you can cut off the tilt back wheels and axle and have a fabricator either cut off the current legs and build some new legs to attach your casters to, or you can attach your casters to the bottom of the existing legs. Its important to note that using the existing legs will make your existing smoker 5-6 inches taller, depending on the wheels you choose. On the new models of that cooker we have changed the wheel configuration to 4 1/2" casters and done away with the tilt back style of moving it around.
Head Pitmaster In Charge, Superior Smokers