Can I use pine needles for a filler in large planter boxes?

I am making planter boxes that go all around our mobile home for keeping the warmth in in the winter and flowers the rest of the year. Would it be all right to put pine needles (we have an abundance of them)in the bottom part of the boxes. Our boxes will probably be about 2 feet tall so if we put soil or planter mix in the whole thing it would definately "break the bank". If we could put pine needles about one foot up, it sure would be cheaper. Should I put a plastic bag between the pine needles and the soil. Should I put rocks in the bottom of the planter boxes for drainage. Someone please HELP! I don't want to do all this and the plants die. Thanks, Carole