Do I need a Gate driver on a Power Mosfet if its working without it?
There is nothing wrong with driving a FET like this if there is no need to PWM.

What I would add is


Add a series gate resistor ( ~100R)
consider adding a 15V zener gate-source just incase there are some transients. You do not want to burn the gate region out 


NOTE: you might want something bigger than just a Zener on the gate. TVS maybe. its dependent where exactly the FET sits with regards to indirect lightning. The DO160 is not very forgiving.