There are boxes that you can use that has the partition in them to keep the interference down. The trick, possibly for you is to make sure the lines where they run parallel with each other is keeping them separated at a MINIMUM of 6". The low voltage guys I have worked with preferred 12" and more, some wanting 2' separation. If the walls are still open it should not give you no trouble then. When you do pass by a line voltage wire, use an extra foot or two and run the low voltage across the line voltage at a 90 degree angle, this will minimize the "crosstalk" where the cables meet.
First you need to figure out the parts you need. Turn the power to the circuit off and remove the outlet. You need to figure out the gauge of the existing wiring. Since it is a 30 amp circuit, the wire should be 10 gauge, so my answer will mostly assume that.
Now you can go to the store and buy a 20 amp outlet, a face plate, a 20 amp breaker, and a breaker blank cover. Make sure you buy a breaker that is compatible with your panel. Check the outlet to make sure it can handle the wire gauge you have. If you can't find a suitable outlet that can handle 10 gauge wire, then you'll need a couple small pieces of 12 gauge wire, or a short piece of nonmetallic sheathed cable that you've stripped, and some wire nuts.
Back home: Turn off your main breaker and remove the cover from your breaker panel. Disconnect the wires going in to the existing breaker and remove the breaker. Install the new breaker and connect the black wire to the breaker. Find the bus bar where all of the white wires are connected and connect the red wire there. Put the cover back on and use the breaker blank to cover the empty spot you created from removing the double breaker.
Back at the outlet: If your outlet can't take a 10 gauge wire, use the 12 gauge wire to create pigtails: cut a black wire to about 8 inches, strip about 1 1/4 inches of insulation off each end, and use a wire nut to attach it to the 10 gauge black wire. Repeat with white (attach to red) and ground. Connect the black wire to the HOT terminal on the outlet, the white/red wire to the NEUTRAL, and the ground to the ground screw. Then push it all in to the box and put the cover on.
Best Answer
Yes, 120V and 240V can cohabitate. Both of those are classified as Class 1 circuits. The highest voltage present in the box will be 240V, and with any normal wiring (NM, THHN in conduit, MC, etc.) all the wiring will have insulation rated well above that voltage.
However, depending on the plug on your charger, it may not fit in half a 2-gang.