Indoor Use and Outdoor Use
Plywood for Marine Use
Marine ply is also going to have more plies than typical construction ply, you want to be on the look out for higher numbers, greater than 7 in my opinion. Marine ply is going to be lighter than ext ply and especially pressure treated ply. For your boat I would go with the Home Depot pressure treated varieties. Your best bet is to get 2 sheets of 3/4 pt ply, let them dry for a week, then glue them together.
Attaching Luan Plywood to Concrete
Attaching Luan to Concrete Floors, is possible if you first overlay the concrete with a think material such as plywood, then use the Laun Material overtop of that. You should use fasteners to attach the thicker plywood pieces to the floor. The best option when using fasteners is to use nails or cememt nails. If you're using the nails made of cement you must first make sure that all the heads of the nails are covered in a putty or smooth finish. The reason for this is that the nail's hard top surface over time will destroy the the laun board material.