Btw, is there a bonus series for hoth?

We haven't skipped any side quests (though we haven't done all heroics). I think the problem is that he's getting an exp penalty due to him not being a subscriber. Maybe he also gets less exp when playing with a higher level character? (I am 41 at the moment)

I'm playing the game with a friend. I'm a subscriber and he isn't. The problem is that we are now supposed to go to a planet that is for level 41 and he is only 37. He's only getting further and further behind. What is the quickest way for him to catch up?