5/8 ply sandwich wall construction?

[Ford340b]

I am building a 7x10x5 high square drop style trailer. Would using a wall construction technique of luan + 5/8 ply + luan + filon be strong enough? I am going to have two splices per side. I plan on using 1/2 polysio foam in the wall voids. Here's a picture of my sub frame that will have a leaf sprung 3500# axle.

 

[Tony Latham]

I don't think you want dead air in the voids, for fear you may get condensation. It would help, of course, if the voids were on the outside wall.

Someone once wrote this in a book about building teardrops:

The box stores sell a thin, generic plywood called luan (or lauan), which is produced in several Asian countries. The term typically refers to plywood that is 1/4” or, less commonly, 1/8” thick. Historically, it was made for interior door sheathing. It’s a mystery from one bunk to the next what the wood is, what glue was used, and how many internal voids it has.

I might suggest considering 1/4" subfloor plywood. Here, in the middle of Idaho, it's cheaper than 1/4" AC with much smaller voilds

Just a couple of thoughts.

Tony