I'm trying to use a Crobat that Uses Mean Look, then switch out with U-turn and set up with a Durant w/ Truant that'll use Entrainment. Would that work?
No. Because the Pokémon switched out, the effects of moves are removed. However, using Baton Pass will keep Mean Look in effect. Though in this case you won't be able to deal damage on switch out.
Unfortunately No This will not work "The effect only applies as long as the Pokémon that used it remains in battle."(http://bulbapedia.bulbagarden.net/wiki/Mean_Look_(move))
Also, what Pokemondb.net user WoonderWaffle said is also incorrect according to Bulbapedia.net. Pokemon that switches out using Baton Pass does not keep the effects of Mean Look.
"If a Pokémon traps a target with Mean Look and then switches with Baton Pass the target will no longer be trapped." (http://bulbapedia.bulbagarden.net/wiki/Mean_Look_(move))
This link http://bulbapedia.bulbagarden.net/wiki/Baton_Pass_(move) has more information on Baton Pass