Please help me power level Axton Zero to 60

Hi, I used to play this game on xbox 360 and lost my 70 Axton and 65 Zero when I switched to the handsome edition. I’m looking to bring them both back up to at least 60 and could use some help. I have never really power levelled in this game before, but I don’t think I can stand to do it the long way this time. Anyone experienced in power levelling willing to help me out I would greatly appreciate it. My Axton is currently 43, and my Zero is currently 11.
PSN: Enderseeker
Thanks in advance!