What I'd be most concerned with is the self watering feature. You'd have to make sure all water is out of the PVC pipes. The table and soil alone should be fine if there's no water. You could always insulate the whole thing with rigid Styrofoam sheets

Don't know what zone you're in but it might be wise to remove some of the soil down to the bottom so freezing moisture expansion/heave of the soil doesn't crack the table. You don't have the earth around your garden area to insulate your planting soil and it will freeze faster than an inground garden.

Let the water drain out of everything, soil and pipes, then cover it.