Houseboat made from locally sourced plywood

Hi guys I am thinking about building a catamaran shaped houseboat 40' x20' using locally sourced plywood and fiberglass/epoxy.

The local supplier has Birch 1/2" and 3/4" plywood but they are unable to tell me with any confidence if it's exterior or interior rated and if the glue is WBP. They claim that it can be used for exterior projects as long as it's sealed with paint or varnish. They also sell a marine grade plywood 3/4" made by consmos a Chinese manufacturer but they don't know what type of wood it is, which makes me nervous that it truly is marine grade. On inspection the Birch appears to be higher quality with no obvious voids or defects.

I'm thinking about using the Birch 1/2" to make the bulkheads and hull panels since I think the 3/4" marine grade would be too heavy. Since I am unsure of the quality of the Birch as well I was thinking of sealing all the bulkheads and hull panels inside and out with both epoxy resin and fiberglass cloth.

If the birch plywood is properly sealed with fiberglass cloth both inside and outside, could I still have issues with the Birch? Should I go with the marine grade even though it'd be much heavier and the quality is questionable as well?

Cut a piece and boil hard for 30 minutes.

Interior glues are typical and won't stand up to the test.

Birch is heavy plywood, the only "marine grade" ply of similar weight is meranti ply, all others are lighter. If the gluelines on the birch are reddish brown, it has exterior glue. Properly sealed with epoxy it will be ok.
If the "marine grade" looks like regular construction ply it's fir.

The marine grade plywood is made by consmos a Chinese manufacturer, if that makes a difference...

Still boil test it all.