Look for some square headed stainless steel fasteners that is made in 315 stainless steel and used on most decking jobs now. These can also be purchased at most of the lumberyards that sell a lot of the pressure treated lumber or I buy them at the hardware store since we live in salt water.

In most cases if you are using epoxy for glue, the fasteners are mostly to hold parts together until the glue dries, or so says many folks, of course not me.

BUt when you say sheet metal screws I think of the ones with the flanged top head larger than what I know as a pan head. There are many flat head so called stainless steel screws also around but most that are purchased in the hardware stores here are 18-8.