I would like to know:
If I do the Claptrap DLC in playthrough 2 and farm the chest-room. Will the items be locked ot the level I did the DLC or will they scale to my characters level and I can farm them through Playthrough 2 up to levle 69?
It’s okay for you to finish the Claptrap DLC now and come back to it later. All loot sources will scale to your level after reaching the Destroyer in PT2. So yes, you can farm the Gift Shop through various levels since the loot will always scale to either your current level or ~2 levels below your current level.