An assembly for utility truck bodies having metal and/or composite reinforcement(s) and/or foam reinforcements and/or honeycomb reinforcement/ and/or wood reinforcements encapsulated within a thermoformed thermoplastic, or thermoset or fiber-reinforced thermoset walking surface floor structure of the truck bed assembly or other composite floor structure with attachable components and junctions, e.g., sidepack(s), and methods of making the same are provided.