How to level up quickly

Go to the location shown in the map below
Once you are there,save the game
Equip the Rocket launcher or any other explosives you have and blow up the 3 trucks.You will get 150xp for destroying the trucks+additional xp for killing nearby enemies.Load last save and repeat.This way you can earn about 170xp per 10secs or about 1k xp/minute.

Pretty much that's it.Thanks for reading.