You may have more trouble finding a glue that will stick to the foam, is the foam a "pick and pluck" soft type, or something harder? check what glues are recommend for this, then e-mail Ikelite and see if they are OK.
When you get a glue that you are happy with, dont forget to remove all the O-rings that you can and put them in a sealed plastic bag, do the glueing in a well ventilated room and allow the the glue to completely dry befor re assembling your rig. The glues fumes can play havoc with you and the O-rings.
Can I suggest that you use VELCRO for attaching your converter inside the housing, you can buy it in strips, cut to size and it can be removed and re-attached easily.