The box is at my brother's so I can't take pictures. I asked him to take a couple of measurements.
Bottom plate is 1/4 aircraft ply, 8 x 18
Center upright is 1/4 aircraft ply, 8 x 16
The rest of the panels are 3/32 or 1/8 lite ply
The sides are 8 inches at the center upright and 6 inches at the end.

The end where the fuel bottle goes has triangle stock in the corners for strength. The kit stuff is made of particle board, and I used it, but balsa would be my first choice.

The other end has an upright about halfway between the center and end, and a divider for the tool and starter compartments. Just be sure the starter will drop into its compartment. The tool compartment has 1/4 square sticks in the corners, about 6 inches long. The plate with holes for glow driver and other tools glues on top of the sticks. I might lower this by an inch if I was building another.