I'm using two layeres of 1/8" on the exterior with the grain on the outer surfaces running from sise to side... Should be a piece of cake.
However... I used one layer of 1/8" maple on my interior... 1/2 sheet on the hatch and a full sheet in the cabin.
I wanted the exposed grain to run lengthwise on the interior and it was a fight, but I took my time by going one spar at a time, glueing each spar as I approached the front of the trailer.
I did have a wormhole on the backside of the plywood, which ran sideways go BANG!!!
Luckily, the skin on the interior side of the cabin didn't go BANG too, right where the worm hole was, but it did develop a small facet at that point.
I was able to insert aditional blocking in the spar area and temporary interior blocking inside the cabin to make the 1/2" long facet disapear.
I only used glue and relied on the length of the maple plywood to lock the ceiling to the spars and spar blocking along the walls.