-- Last Updated: Mar-19-13 3:50 PM EST --
... minimize producing stress in a potentially damaging orientation, putting the tie-down points a little up the sides of the hull would be best. That way, the direction of pull (which will be primarily upward) will be less "straight out" from the hull and tend to be more in-line with the hull. This will also cause your anchor patches to be stressed less in tension and more in the direction of shear, and in terms of adhesive strength this will be enormously stronger (though it may not matter).
It'll be interesting to see what others say, but I'd be inclined to avoid pulling straight up on any part of the hull that is well inside the margins of the foam core. However, I bet that the junction of the inner and outer layers along the edges of the foam core would be a pretty strong place, since it's naturally reinforced with the inner layer being oriented almost cross-wise to the outer layer right along the edge of the core. Attaching your anchor patches right along that bevel might be as good or better than partway up the sides as described above.