It is just my opinion, OSB is heavy and probably would also give up some vapors to inside.
I glued 1/8" baltic birch plywood inside my foamie trailer build.
Am really curious about your fiberglass epoxy lamination, where are you getting your epoxy from?
There must be a chemical company in Quebec who would have a very good price epoxy, are you getting that from them?
One distributor I saw is this
http://www.hl-plasto.com/Default.asp but I know there is a
manufacturing or maybe blending company in Quebec that makes epoxy.
I forgot their name (Chimique ..? ).