Place one wooden wine crate on its side with the top opening facing you. Stack the second crate on top of the first one in the same manner.
Drive a decorative head wood screw — using a screw gun — through each corner of the side of the top crate that is resting on the top side of the bottom crate to fasten the two crates together.
Wipe off the two crates with a tack cloth to make sure they are free of dust or debris. Spray the crate assembly with a clear coat of spray lacquer. Allow the lacquer to dry for at least four hours and apply a second coat. Let the second coat dry for 24 hours.
Turn the assembly over so that the bottom of the assembled crates is facing up. Center one caster in each corner of the bottom. Use a screw gun to drive the screws included with the casters through the mounting holes into the wooden crate. Turn the assembly upright so that it rests on the casters.