Clear oasis as frequently as you can and farm them frequently.
25% oasis gives you 4k res, while 50%(or 25% + 25%) gives you 8k res. I have found the best way to do so is send 2k offensive troops with hero. Your losses will usually be less that your bounty.
Its a great way to earn hero experience and attacker points as well, and trust me you can win an attackers medal by just clearing oasis for a week.
You can have a very high level hero and a pretty profile if you do this often.