bathroom remodel

Just wondering if I should put moisture barrier behind tub surround

If the manufacturer calls for one, then yes. If it were tile, yes, But, a surround is, at least supposed to be totally waterproof. The reason for the vapor barrier is to prevent condensation on the back causing the potential for rot and mold. But to get that, you have to have moisture get there. A surround shouldn't. It won't hurt IMHO, though.