glue,screws,silicone,resin, bracing would be needed if there are big pieces of wood like a top and bottom that dont have much support from the port for example, and cause box to flex, or just flat out break
When you say "truck", do you mean like an SUV or an actual pickup truck. Usually the preferred setup for a pickup is subs forward with port up. Never seen a setup with the port facing back towards the cab wall, would waste too much space because the box would have to be atleast a port's-width away from the rear wall or you'd get loading issues.