I will be flat towing (4 wheels down) behind my RV. Battery is off. So tow installer was not sure if I need to leave key in ignition, with ignition off, in order for steering wheel not to lock.

Yes the key will have to stay in the ignition

Read your owners manual to see if Ford approves flat towing.

Vehicles with an Automatic Transmission but No Push Button Start System Note: There must be battery power to properly move the transmission’s internal components to position N in Step 3. In addition, moving the gear shift to position N without first turning the ignition to the on (II) position limits the towing capability to 35 mph (56 km/h) and 50 miles (80 kilometers). 1. Release the parking brake. 2. Turn the ignition to the on (II) position. 3. Press the brake pedal, then move the gear shift to position N. 4. Wait for TRANSMISSION READY to appear in the multi-function display, then turn the ignition to the off (0) position and release the brake pedal. 5. Disconnect the negative (black) cable from the battery. (The anti-theft system does not function until the battery cable is reconnected.) See Changing the vehicle battery in the Maintenance chapter when disconnecting and reconnecting the battery cable. The maximum towing speed is 70 mph (113 km/h). There is no limitation on towing distance. When done towing, start the engine within 15 minutes of reconnecting the battery cable. When reconnecting that cable, tighten it until it is snug against the terminal. Be careful not to over-tighten.

Thank you and yes I have read the Focus Manual. No mention of key in or out. I do not have push button start.

Once the battery is disconnected the is able to go fully back and removed. My 2015 focus se with sport package does not have a locking steering wheel. To check if yours is different go thru the procedure and then turn the wheel one rotation in both directions if it don’t lock your good.