General Wolfe - Construction Materials Questions

[Wrench]

Have decided to build the hull using a similar system to the Admiral's Iron Duke. Wood for frame and hull shell. Cover in light fiberglass. Will also likely plate with some form of thin metal. Read thru the pages covering the hull but did not see type or thickness of the wood listed.
Need to start with frames. My choices would be a plywood for stability vs a solid piece of wood. Thinking that I would use 1/4 inch or 3/8 inch. Frame spacing is two inches at bow and stern, midships is a box and overall model length at 42 inches.
Also, a false top deck at 1/8th inch.
Reasonable cost materials via Lowe's/Home Depot include the following plywoods in the above thicknesses.
Luan - Very inexpensive, dimensionally stable (consistantly flat) compared to other materials viewed.
Oak or Birch ply. About 1/3rd more in cost and would have to look through the supply to find flattest available.
Concern is how well these would work. I like the luan as I've used it for other projects but am concerned with how it would do as a boat even covered in fiberglass.
Would appreciate opinions and if I am totally out in left field.

Just noticed I should have filed this elsewhere. please move as needed.