If you have lots of luggage, consider a coach or taxi to Gatwick for easier boarding

https://www.scribd.com/document/1077066259/Heathrow-to-Gatwick-Airport-Transfers-Coach-Taxi-or-Train-174457

If you have lots of luggage, consider a coach or taxi to Gatwick for easier boarding. Trains can be crowded at peak times; board at the front or rear cars for more space.