If coming from the south, many coastal towns have direct trains to Gatwick

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

If coming from the south, many coastal towns have direct trains to Gatwick. Check Southern and Thameslink routes from places like Worthing, Lewes, and Eastbourne.