I find my bags dry out quite quickly as they are designed not to hold too much water. I did put a fork through mine in a couple of places as I hadnt thought about them being designed to drain. I certainly find that the strawberries in them need watering.
I would also consider putting posts in each corner and nailing the bag to the post, this provides support to the sides of the bags which will tend to slump down a bit and they can provide support for netting if required or to support an old show screen and act as a cloche. I tried it with canes but they are just not strong enough.