Keystone interior wall thickness?

It is 1/8" luan (or there about) with 1.5" (or there about) solid foam, then another layer of luan and then filon for outside.
I have hung coat hooks, magazine racks, etc with no problems to these walls. I have found that using 1/2" wood screws and no drilling for pilot holes works best. Do not use screw gun bit just slow firm pressure with screwdriver to get screws to bite into the wood. Do not over tighten, just a little beyond snug will keep things solid. Make sure you limit the weight of whatever you are using hooks or racks for.