Will these mount at the factory mirror points with no drilling?

These are designed to mount at factory attachment locations. Confirm the mounting hole pattern matches your specific model year before final installation.

Do the LED markers stay lit all the time or only when the turn signal is active?

The LED side markers wire into your vehicle's turn signal circuit, so they illuminate when you activate the corresponding turn signal.

Are these mirrors stable at highway speeds with a trailer in tow?

Manual towing mirrors are engineered for towing loads. Once adjusted and locked, they hold position under normal highway conditions — verify they're fully secured before towing.