I'm not too sure you should even be considering gluing these parts together.

Nylon is so much stronger than the foam that even if you had a "perfect" adhesive, an odd tug on the nylon would rip the foam. Putting a slit in the foam to provide more gluing area would really just give a weaker foam part, with more potential for it being easily damaged in the future.

Why not sew the straps onto the foam? A long needle with some thread of the size and weight used for sewing on buttons should do a good job.

If you put a short piece of fabric, or perhaps a cut-off piece of your nylon strap on the front side of the foam you can stitch through a "sandwich" of nylon-foam-nylon. The thread would be going in a straight line through the foam and would not rip it because of the reinforcement of the nylon straps on both sides. Just pull your stitches tight enough to barely compress the foam and you should have a really strong attachment.

If you have covered your foam pads with a layer of spandex or lycra (held on with a bit of 3M's #77 spray glue) then just stitch through these fabric layers. Your pad will have a bit of a tufted look -- and that could be really sharp. The lycra cover on the pad will protect it from abrasion. The sewing will keep the lycra in place (along with your nylon strap) should the glue eventually give in to the effects of sea and sky.

hope this helps

PGJ