There are purpose made fixings for this job called "big foot". They are available with male or female (stud or tube nut) protrusions and I think stainless would be a better option. The flange plate on these fixings is usually perforated to assist adhesion. I do not know how to calculate pull out strength, but would suggest the better way might be to rebate the the outer skin for the footplate. drill through for the stud bond the fixing in from the outside and then glass over the rebated area. The second skin of fibreglass applied to a precured skin does not adhere as well as a single skin laid up in several layers. If the studs you use are M6, I may be able to give you a few in stainless steel. If you google Bigfoot fixings they may be able to give you some technical advice. Good luck.G.